Hollow microspheres

ABSTRACT

Hollow glass microspheres made from a low heat conductivity glass composition containing a high vacuum and a thin metal coating deposited on the inner wall surface of the microspheres are described. The hollow glass microspheres are used to make superior insulation materials in the construction of highly efficient solar energy collectors. 
     The hollow glass microspheres can also be made to contain a thin transparent or reflective metal coating deposited on the inner wall surface of the microspheres by adding to the blowing gas small dispersed metal particles and/or gases of organo metal compounds and decomposing the organo metal compounds. 
     The hollow glass microspheres can be made from low heat conductivity glass compositions. The microspheres can be used to make improved insulation materials and composites and insulating systems. 
     The hollow glass microspheres can be used as filler materials in plastics, in plastic foam compositions and in concrete and asphalt compositions. 
     The hollow glass microspheres can also be made in the form of filamented glass microspheres with a thin glass filament connecting adjacent glass microspheres.

This is a division, of application Ser. No. 059,297, filed July 20,1979, which application is a continuation-in-part of applicant'sapplications Ser. Nos. 937,123 and 944,643, filed Aug. 28, 1978 andSept. 21, 1978, respectively all abandoned.

SUMMARY OF THE INVENTION

The present invention relates to hollow microspheres made from inorganicfilm forming materials and compositions and particularly to hollow glassmicrospheres and to a process and apparatus for making the microspheres.

The present invention particularly relates to hollow glass vacuummicrospheres having a thin transparent metal coating deposited on theinner wall surface of the microsphere.

The present invention also relates to hollow glass vacuum microsphereshaving a thin reflective metal coating deposited on the inner wallsurface of the microsphere.

The present invention relates to hollow glass microspheres for use as afiller material in plastics, in plastic foam compositions and inconcrete and asphalt compositions.

The present invention relates to a method and apparatus for using acoaxial blowing nozzle to blow microspheres from liquid glasscompositions comprising subjecting the microsphere during its formationto an external pulsating or fluctuating pressure field having periodicoscillations, said pulsating or fluctuating pressure field acting onsaid microsphere to assist in its formation and to assist in detachingthe microsphere from said blowing nozzle.

The invention particularly relates to a method and apparatus for blowingthe microspheres from inorganic film forming materials or compositionsand particularly to blowing microspheres from a molten glass using acoaxial blowing nozzle and an inert blowing gas or a metal vapor to blowthe molten glass to form a hollow glass microsphere.

The invention also relates to a method and apparatus for blowing themicrospheres from liquid glass compositions using a coaxial blowingnozzle and a blowing gas or a blowing gas containing dispersed metalparticles and/or an organo metal compound to blow the liquid glass toform a hollow glass microsphere. The metal particles deposit and/or theorgano metal compound decomposes to deposit a thin transparent orreflective metal coating on the inner wall surface of the microsphere.

A transverse jet is used to direct an inert entraining fluid over andaround the blowing nozzle at an angle to the axis of the blowing nozzle.The entraining fluid as it passes over and around the blowing nozzleenvelops and acts on the molten glass as it is being blown to form themicrosphere and to detach the microsphere from the coaxial blowingnozzle. Quench means are disposed close to and below the blowing nozzlesto direct a quench fluid onto the microspheres to rapidly cool andsolidify the microspheres.

The present invention specifically relates to the use of the hollowglass microspheres and the hollow glass vacuum microspheres in themanufacture of superior insulation materials for use in construction ofhomes, factories and office buildings and in the manufacture of productsin which heat barriers are desired or necessary and in particular in theconstruction of highly efficient solar energy collectors.

The present invention specifically relates to the use of the hollowglass microspheres as filler materials in syntactic foam systems.

The present invention also relates to a method and apparatus for makingfilamented glass microspheres with thin glass filaments connectingadjacent microspheres and to the filamented microspheres themselves.

The hollow glass microspheres of the present invention, depending ontheir diameter and their wall thickness and the particular glasscomposition from which they are made, are capable of withstandingrelatively high external pressures and/or weight. Hollow glassmicrospheres can be made that are resistant to high temperatures andstable to many chemical agents and weathering conditions. Thesecharacteristics make the microspheres suitable for a wide variety ofuses.

BACKGROUND OF THE INVENTION

In recent years, the substantial increases in the energy costs ofheating and cooling has encouraged the development of new and betterinsulation materials and many new insulation materials have beendeveloped in an attempt to satisfy this need. The same increases inenergy costs have provided an incentive for adapting solar energy as ameans for providing heating and cooling. The attempts to adapt solarenergy for these uses would become more practical with the developmentof improved and more efficient insulating materials.

In recent years, the substantial increases in costs of basic materialssuch as plastics, cement, asphalt and the like has also encourageddevelopment and use of filler materials to reduce the amount and cost ofthe basic materials used and the weight of the finished materials. Oneof the newly suggested filler materials utilizes hollow glassmicrospheres. The known methods for producing hollow glass microspheresfor use as filler materials, however, have not been successful inproducing microspheres of uniform size or uniform thin walls which makesit very difficult to produce filler and insulation materials ofcontrolled and predictable physical and chemical characteristics andquality.

One of the newly developed insulation materials utilizes packed glassmicrospheres, the outer surface of which microspheres are coated with areflective metal and a vacuum is maintained in the interstices areabetween the microspheres. The outer reflective metal coating minimizesheat transfer by radiation and a vacuum maintained in the intersticesarea minimizes heat transfer by gas conduction. Insulation materials,however, made from these types of microspheres possess several inherentdisadvantages. It has been found to be difficult if not impossible inmany applications to maintain the vacuum in the interstices area betweenthe packed microspheres and loss of this vacuum increases the heattransfer by gas conduction. It has also been found very difficult andcostly to deposit a relatively thin uniform film of reflective metal onthe outer surface of the microspheres. Even where a suitable thinreflective coating of metal has been deposited on the outer surface ofthe microspheres, it is found that as the coating wears the area ofpoint to point contact between the microspheres increases whichincreases heat transfer by solid conduction between the microspheres andthe wearing of the reflective metal coating necessarily causesdeterioration of the reflective metal surface and further increases heattransfer by radiation.

The known methods for producing hollow glass microspheres have not beensuccessful in producing microspheres of relatively uniform size oruniform thin walls which makes it very difficult to produce insulationmaterials of controlled and predictable characteristics and quality.

One of the existing methods of producing hollow glass microspheres foruse as insulating materials, for example, as disclosed in the Veatch etal U.S. Pat. No. 2,797,201 or Beck et al U.S. Pat. No. 3,365,315involves dispersing a liquid and/or solid gas-phase precursor materialin the glass material to be blown to form the microspheres. The glassmaterial containing the solid or liquid gas-phase precursor enclosedtherein is then heated to convert the solid and/or liquid gas-phaseprecursor material into a gas and is further heated to expand the gasand produce the hollow glass microsphere containing therein the expandedgas. This process is, understandably, difficult to control and ofnecessity, i.e. inherently, produces glass microspheres of random sizeand wall thickness, microspheres with walls that have sections orportions of the walls that are relatively thin, walls that have holes,small trapped bubbles, trapped or dissolved gases, any one or more ofwhich will result in a substantial weakening of the microspheres, and asubstantial number or proportion of microspheres which are not suitablefor use and must be scrapped or recycled.

Further, the use of conventional fiberglass insulation is beingquestioned in the light of the recently discovered possibility thatfiberglass of certain particle size may be carcinogenic in the same orsimilar manner as asbestos. The use of polyurethane foams,urea-formaldehyde foams and polystyrene foams as insulating materialshave recently been criticized because of their dimensional and chemicalinstability, for example, a tendency to shrink and to evolve the blowinggases such as Freon and to evolve unreacted gases such as formaldehyde.

In addition, in some applications, the use of low density microspherespresents a serious problem because they are difficult to handle sincethey are readily elutriated and tend to blow about. In situations ofthis type, the filamented microspheres of the present invention providea convenient and safe method of handling the microspheres.

It is also been suggested that hollow glass vacuum microspheres having areflective metal deposited on the inner wall surface thereof be used tomake insulating materials. There have been several methods suggested formaking this type of hollow vacuum microsphere but to date none of theknown methods are believed to have been successful in making any suchmicrospheres.

Further, the existing methods practiced to produce hollow glassmicrospheres usually rely on high soda content glass compositionsbecause of their relatively low melting points. These glasscompositions, however, were found to have poor long term weatheringcharacteristics.

Thus, the known methods for producing hollow glass microspheres havetherefore not been successful in producing microspheres of uniform sizeor uniform thin walls or in producing hollow glass microspheres ofcontrolled and predictable physical and chemical characteristics,quality and strength.

In addition, applicant found in his initial attempts to use an inertblowing gas to blow a thin molten glass film to form a hollow glassmicrosphere that the formation of the glass microsphere was extremelysensitive and that unstable films were produced which burst into minutesprays of droplets before a molten glass film could be blown into amicrosphere and detached from a blowing nozzle. There was also atendency for the molten glass fluid to creep up the blowing nozzle underthe action of wetting forces. Thus, initial attempts to blow hollowglass microspheres from thin molten glass films were unsuccessful.

The attempts to use solar energy for heating and/or cooling have beenhampered by the rapid increase in rate of heat loss to the surroundingatmosphere that occurs when the outside temperature is below 32° F. orwhen the operating temperature, i.e. outlet heat exchange medium of thesolar energy collector, approaches 160° F. The lower the outsidetemperature or the higher the operating temperature of the solar energycollector, the greater the heat loss and the lower the efficiency of thesolar collector. It has been found that with the commercially attractiveinsulation technology available that reasonably priced solar collectorshave only been operated efficiently at outside temperatures above 32° F.and at operating temperatures below 160° F. Though this is sufficientfor heating hot water for bathing and laundry uses and for providinghousehold heat, it is not sufficient for heating at outside temperaturesbelow 32° F. or for air-conditioner applications.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a process and anapparatus for making hollow glass microspheres.

It is another object of the present invention to utilize the hollowglass microspheres of the present invention in the manufacture ofimproved insulating materials and insulating systems.

It is another object of the present invention to make hollow glassmicrospheres for use as and/or in filler materials.

It is another object of the present invention to produce hollow glassmicrospheres having uniform thin walls which walls are substantiallyfree of trapped gas bubbles or dissolved gases or solvents which canform bubbles and/or escape.

It is another object of the present invention to produce hollow glassmicrospheres which are substantially resistant to heat, chemical agentsand alkali materials.

It is still another object of the present invention to utilize thehollow glass microspheres in the manufacture of syntactic foam systemsand/or molded forms or shapes.

It is another object of the invention to produce hollow glassmicrospheres having thin walls of a low heat conductivity glass.

It is another object of the present invention to produce hollow glassmicrospheres having a low heat conductivity gas contained within themicrosphere.

It is another object of the present invention to produce hollow glassvacuum microspheres having deposited on the inner wall surface thereof athin transparent metal coating.

It is another object of the present invention to produce hollow glassvacuum microspheres having deposited on the inner wall surface thereof alow emissivity reflective metal coating.

It is another object of the present invention to produce in aneconomical simple manner hollow glass microspheres which aresubstantially spherical in shape, uniform in size, wall thickness, andstrength and thermal insulating characteristics.

It is another object of the present invention to utilize the hollowglass microspheres of the present invention in the manufacture ofsuperior insulation materials and/or for use in the manufacture offormed wall panels.

It is still another object of the present invention to utilize thehollow glass microspheres in the construction and manufacture ofsuperior insulating materials for high temperature applications and theretardation of fires.

It is another object of the present invention to produce hollow glassfilamented microspheres with a thin glass filament connecting adjacentglass microspheres.

It is still another object of the present invention to utilize thehollow glass microspheres of the present invention in the manufacture ofsuperior insulation materials for use in the construction of highlyefficient solar energy collectors.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to hollow glass microspheres and to aprocess and apparatus for making the microspheres. The present inventionmore particularly relates to the use of hollow glass microspheres in themanufacture of superior insulation materials and systems and improvedfiller materials.

The microspheres are made from a glass composition or a low heatconductivity glass composition and can contain a low heat conductivitygas. The microspheres can also be made to contain a high vacuum and athin metal coating deposited on the inner wall surface of themicrospheres.

The microspheres can also be made to contain a gas at above or below orat about ambient pressure and a thin metal coating deposited on theinner wall surface of the microspheres.

The metal coating, depending on its thickness, can be transparent orhighly reflective. The use of a high vacuum and a reflective metalcoating substantially improves the insulating characteristics of themicrospheres.

The use of microspheres with a reflective metal coating but without ahigh vacuum still improves the heat insulating characteristics of themicrospheres.

The glass microspheres of the present invention can be used to form aheat barrier by using them to fill void spaces between existing walls orother spaces and by forming them into sheets or other shaped forms to beused as insulation barriers. When used to form insulation barriers, theinterstices between the microspheres can be filled with a low heatconductivity gas, foam or other material all of which increase the heatinsulation characteristics of the materials made from the microspheres.

A particular and advantageous use of the hollow glass vacuummicrospheres is to make transparent and reflective insulation materialsfor the construction of improved solar energy collectors.

The hollow glass microspheres of the present invention are made byforming a liquid film of molten glass across a coaxial blowing nozzle,applying an inert gas or metal vapor at a positive pressure on the innersurface of the glass film to blow the film and form an elongatedcylinder shaped liquid film of molten glass which is closed at its outerend.

The hollow glass microspheres of the present invention can also be madeby applying a gas or a gas containing dispersed metal particles and/or agaseous organo metal compound at a positive pressure to the innersurface of the glass film to blow the film and form an elongatedcylinder shaped liquid film of glass which is closed at its outer end. Abalancing but slightly lower gas pressure is provided in the area of theblowing nozzle into which the elongated cylinder shaped liquid glassfilm is blown.

A transverse jet is used to direct an entraining fluid over and aroundthe blowing nozzle at an angle to the axis of the blowing nozzle. Theentraining fluid as it passes over and around the blowing nozzle and theelongated cylinder fluid dynamically induces a pulsating or fluctuatingpressure field at the opposite or lee side of the blowing nozzle in thewake or shadow of the blowing nozzle. The fluctuating pressure field hasregular periodic lateral oscillations similar to those of a flagflapping in a breeze.

The transverse jet entraining fluid can also be pulsed at regularintervals to assist in controlling the size of the microspheres and inseparating the microspheres from the blowing nozzle and the distance orspacing between micospheres.

The entraining fluid envelops and acts asymmetrically on the elongatedcylinder and causes the cylinder to flap, fold, pinch and close-off atits inner end at a point proximate to the coaxial blowing nozzle. Thecontinued movement of the entraining fluid over the elongated cylinderproduces fluid drag forces on the cylinder and detaches the elongatedcylinder from the coaxial blowing nozzle to have it fall free from theblowing nozzle. The surface tension forces of the molten glass act onthe now free, entrained elongated cylinder and cause the cylinder toseek a minimum surface area and to form a spherical shape.

Quench nozzles are disposed below and on either side of the blowingnozzle and direct cooling fluid at and into contact with the moltenglass microspheres to rapidly cool and solidify the molten glass andform a hard, smooth hollow glass microsphere. Where a metal vapor isused as a blowing gas to blow the microspheres, the quench fluid coolsand condenses the metal vapor and causes the metal vapor to deposit onthe inner wall surface of the microsphere as a transparent metal coatingor a thin reflective metal coating.

In one embodiment of the invention, the microspheres are coated with anadhesive or foam filler and flattened to an oblate spheroid or agenerally cellular shape. The microspheres are held in the flattenedposition until the adhesive hardens and/or cures after which themicrospheres retain their flattend shape. The use of the flattenedmicrospheres substantially reduces the volume of the interstices betweenthe microspheres and significantly improves the thermal insulatingcharacteristics of the microspheres.

The microspheres can be made from glass compositions selected for theirdesired optical and chemical properties and for the particular gaseousmaterial to be contained therein.

Where a gas containing dispersed metal particles is used to blow themicrospheres, a metal layer is deposited on the inner wall surface ofthe microsphere as a thin metal coating. Where a gaseous organo metalcompound is used to deposit the metal layer, a gaseous organo metalcompound is used as or with the blowing gas to blow the microspheres.The organo metal compound can be decomposed just prior to blowing themicrospheres or after the microspheres are formed by, for example,subjecting the blowing gas or the microspheres to heat and/or anelectrical discharge.

The filamented microspheres are made in a manner such that they areconnected or attached to each other by a thin continuous glass filament.The filamented microspheres can also be flattened to produce the oblatespheroids. The filaments interrupt and reduce the area of wall to wallcontact between the microspheres and reduce the thermal conductivitybetween the walls of the microspheres. The filamented microspheres alsoassist in handling and preventing scattering of microspheres,particularly where very small diameter microspheres or low densitymicrospheres are produced. The filamented microspheres have a distinctadvantage over the simple addition of filaments in that the continuousfilaments do not tend to settle in the system in which they are used.

THE ADVANTAGES

The present invention overcomes many of the problems associated withprior attempts to produce hollow glass microspheres and hollow glassvacuum microspheres containing a metal coating deposited on the innerwall surface thereof. The process and apparatus of the present inventionallows the production of hollow glass microspheres having predeterminedcharacteristics such that superior insulation materials and systems andimproved filler materials can be designed, manufactured and tailor madeto suit a particular desired use. The diameter, wall thickness anduniformity and the thermal, strength and chemical resistancecharacteristics of the microspheres can be determined by carefullyselecting the constituents of the glass composition and controlling theinert gas or metal vapor pressure and the temperature, and thetemperature, viscosity, surface tension, and thickness of the moltenglass film from which the microspheres are formed. The inner volume ofthe microspheres may contain an inert low conductivity gas used to blowthe microsphere or can contain a high vacuum produced by condensing ametal vapor used to blow the microsphere. The hollow glass microspheresand the hollow glass vacuum microspheres of the present invention canhave a transparent metal coating deposited on the inner wall surfacethereof which allows sun light to pass through the microspheres butreflects and traps infrared radiations. The hollow glass microspheresand the hollow glass vacuum microspheres can also have a low emissivityhighly reflective metal coating deposited on the inner wall surface ofthe microsphere which effectively reflects light and radiant heat energyand avoids the wear and deterioration that occurs by utilizing an outercoating of a reflective metal caused by point to point contact of themicrospheres with adjacent spheres and/or chemical degradation due tochemical agent in the surrounding atmosphere.

The process and apparatus of the present invention provide a practicaland economical means by which hollow glass microspheres having a highheat insulation efficiency can be utilized to prepare a relatively lowcost efficient insulating material for every day uses.

The process and apparatus of the present invention for the first timeprovide a practical and economical means by which the high heatinsulation efficiency of a vacuum can be utilized to prepare arelatively low cost highly efficient insulating material for commonevery day uses. The present invention also allows the economicalproduction of hollow glass microspheres from a low or high meltingtemperature glass composition which incorporates a radiation barrier andcan be used as an insulating material. The apparatus and process of thepresent invention provide for the production of hollow glassmicrospheres at economic prices and in large quantities. The process andapparatus of the present invention also provide for the production ofhollow glass vacuum microspheres at economic prices and in largequantities.

The process and apparatus of the present invention, as compared to theprior art processes of using a latent liquid or solid blowing agent, canbe conducted at higher temperatures since there is no includedexpandable and/or decompsable blowing agent used. The ability to usehigher blowing temperatures results in for particular glass compositionsa lower glass viscosity which allows surface tension forces to producesignificantly greater uniformity in wall thickness, sphericity anddiameter of the microspheres produced.

The process and apparatus of the present invention allow the use of awide variety of blowing gases and blowing gas materials to be used andencapsulated.

The present invention provides a method for using a metal vapor blowinggas to blow hollow glass microspheres to obtain a high contained vacuumwithin the microsphere. The present invention also allows for theaddition to metal vapor blowing gas small amounts of selected metalvapors, e.g. alkali metal vapors, to getter, i.e. react with trace gasesthat may evolve from the molten glass film as the microsphere is beingformed. The selected metal vapors getter any evolved gases and maintainthe high contained vacuum.

The process and apparatus of the present invention allows the productionof hollow glass microspheres for insulation and/or filler uses havingpredetermined diameters, wall thicknesses, strength and resistance tochemical agents and weathering and gas permeability such that superiorsystems can be designed, manufactured and tailor made to suit aparticular desired use. In addition, the surface of the hollow glassmicrospheres, because of the method by which they are made, do not have,i.e. are free of sealing tips.

The hollow glass microspheres and hollow glass vacuum microspheres ofthe present invention can be used in the design and construction ofsuperior insulating systems for use in combination with solar energycollectors such that the solar energy collectors can be efficientlyoperated at outside temperatures below 32° F. and can be operated atheat exchange medium outlet temperatures above 160° F. such that theyoperate efficiently in the winter and in the summer they can be used tosupply summer air-conditioning needs.

BRIEF DESCRIPTION OF THE DRAWINGS

The attached drawings illustrate exemplary forms of the method andapparatus of the present invention for making microspheres for use inand as insulating materials and/or for use in and as filler materials.

The FIG. 1 of the drawings shows in cross-section an apparatus havingmultiple coaxial blowing nozzle means for supplying the gaseous materialfor blowing hollow glass microspheres, a transverse jet providing anentraining fluid to assist in the formation and detachment of themicrospheres from the blowing nozzles, and means for supplying a quenchfluid to cool the microspheres.

The FIG. 2 of the drawings is an enlarged detailed cross-section of thenozzle means of apparatus shown in FIG. 1.

The FIG. 3 of the drawings is a detailed cross-section of a modifiedform of the nozzle means shown in FIG. 2 in which the lower end of thenozzle means is tapered inwardly.

The FIG. 3a of the drawings is a detailed cross-section of a modifiedtransverse jet entraining means having a flattened orifice opening andthe FIG. 3 nozzle means.

The FIG. 3b of the drawings is a top plane view of the modifiedtransverse jet entraining means and the nozzle means illustrated in FIG.3a of the drawings.

The FIG. 3c of the drawings illustrates the use of the apparatus of FIG.3b to make filamented hollow glass microspheres.

The FIG. 4 of the drawings is a detailed cross-section of a modifiedform of the nozzle means shown in FIG. 2 in which the lower portion ofthe nozzle is enlarged.

The FIG. 5 of the drawings shows a cross-section of an end view of aflat plate solar energy collector using the hollow glass microspheres ofthe present invention.

The FIG. 6 of the drawings shows a cross-section of an end view of atubular solar energy collector using the hollow glass microspheres ofthe present invention.

The FIG. 7 of the drawings shows a cross-section of spherical shapedhollow glass microspheres made into a formed insulation panel.

The FIG. 7a of the drawings shows a cross-section of oblate spheroidshaped hollow glass microspheres made into a formed insulation panel.

The FIG. 7b of the drawings shows a cross-section of oblate spheroidshaped hollow glass filamented microspheres made into a formedinsulation panel in which the filaments interrupt the microsphere wallto wall contact.

The FIG. 8 of the drawings illustrates in graphic form the relationshipbetween the thickness of the thin metal film deposited on the inner wallsurface of the hollow microsphere, the metal vapor blowing gas pressureand the diameter of the microspheres.

DETAILED DISCUSSION OF THE DRAWINGS

The invention will be described with reference to the accompanyingFigures of the drawings wherein like numbers designate like partsthroughout the several views.

Referring to FIGS. 1 and 2 of the drawings, there is illustrated avessel 1, made of suitable refractory material and heated by means notshown for holding molten glass 2. The bottom floor 3 of vessel 1contains a plurality of openings 4 through which molten glass 2 is fedto coaxial blowing nozzles 5. The coaxial blowing nozzle 5 can be madeseparately or can be formed by a downward extension of the bottom 3 ofvessel 1. The coaxial blowing nozzle 5 consists of an inner nozzle 6having an orifice 6a for a blowing gas, an inert blowing gas or metalvapor blowing gas and an outer nozzle 7 having an orifice 7a for moltenglass. The inner nozzle 6 is disposed within and coaxial to outer nozzle7 to form annular space 8 between nozzles 6 and 7, which annular spaceprovides a flow path for molten glass 2. The orifice 6a of inner nozzle6 terminates at or a short distance above the plane of orifice 7a ofouter nozzle 7.

The molten glass 2 at about atmospheric pressure or at elevated pressureflows downwardly through annular space 8 and fills the area betweenorifice 6a and 7a. The surface tension forces in molten glass 2 form athin liquid molten glass film 9 across orifice 6a and 7a.

A blowing gas 10, inert blowing gas, metal vapor blowing gas and/or ablowing gas containing dispersed metal particles, which is heated bymeans not shown to about the temperature of the molten glass and whichis at a pressure above the molten glass pressure at the blowing nozzle,is fed through distribution conduit 11 and inner coaxial nozzle 6 andbrought into contact with the inner surface of molten glass film 9. Theblowing gas or metal vapor exerts a positive pressure on the moltenglass film to blow and distend the film outwardly to form an elongatedcylinder shaped liquid film 12 of molten glass filled with the blowinggas or metal vapor 10. The elongated cylinder 12 is closed at its outerend and is connected at its inner end to outer nozzle 7 at theperipheral edge of orifice 7a. A balancing pressure of a gas or of aninert gas, i.e. a slightly lower pressure, is provided in the area ofthe blowing nozzle into which the elongated cylinder shaped liquid filmis blown. The illustrated coaxial nozzle can be used to producemicrospheres having diameters three to five times the size of the insidediameter of orifice 7a and is useful in blowing low viscosity glassmaterials.

A transverse jet 13 is used to direct an inert entraining fluid 14,which is heated to about, below or above the temperature of the moltenglass 2, by means not shown. The entraining fluid 14 is fed throughdistribution conduit 15, nozzle 13 and transverse jet nozzle orifice 13aand directed at the coaxial blowing nozzle 5. The transverse jet 13 isaligned to direct the flow of entraining fluid 14 over and aroundblowing nozzle 7 in the microsphere forming region at and behind theorifice 7a. The entraining fluid 14 as it passes over and around blowingnozzle 5 fluid dynamically induces a pulsating or fluctuating pressurefield in the entraining fluid 14 at the opposite or lee side of blowingnozzle 5 in its wake or shadow.

The entraining fluid 14 envelops and acts on the elongated cylinder 12in such a manner as to cause the cylinder to flap, fold, pinch andclose-off at its inner end at a point 16 proximate to the orifice 7a ofouter nozzle 7. The continued movement of the entraining fluid 14 overthe elongated cylinder 12 produces fluid drag forces on the cylinder 12and detaches it from the orifice 7a of the outer nozzle 7 to allow thecylinder to fall, i.e. be entrained and transported away from nozzle 7.The surface tension forces of the molten glass act on the entrained,falling elongated cylinder 12 and cause the cylinder to seek a minimumsurface area and to form a spherical shape hollow molten glassmicrosphere 17.

Quench nozzles 18 having orifices 18a are disposed below and on bothsides of coaxial blowing nozzle 5 and direct cooling fluid 19 at andinto contact with the molten glass microsphere 17 to rapidly cool andsolidify the molten glass and form a hard, smooth hollow glassmicrosphere. The quench fluid 19 also serves to carry the hollow glassmicrosphere away from the coaxial blowing nozzle 5. Where a metal vaporis used as a blowing gas to blow the microspheres, the quench fluidcools and condenses the metal vapor to deposit the metal vapor on theinner wall surface of the microsphere as a transparent or reflectivethin metal coating 20. Additional cooling time, if necessary, can beprovided by using a fluidizied bed, liquid carrier or belt carriersystem for the hollow glass microspheres to harden the microspheres withsubstantially little or no distortion or effect on the size or shape ofthe microspheres. The cooled and solidified hollow glass microspheresare collected by suitable means not shown.

The FIG. 3 of the drawings illustrates a preferred embodiment of theinvention in which the lower portion of the outer coaxial nozzle 7 istapered downwardly and inwardly at 21. This embodiment as in theprevious embodiment comprises coaxial blowing nozzle 5 which consists ofinner nozzle 6 with orifice 6a and outer nozzle 7 with orifice 7a'. Thefigure of the drawings also shows elongated cylinder shaped liquid film12 with a pinched portion 16.

The use of the tapered nozzle 21 construction was found to substantiallyassist in the formation of a thin molten glass film 9' in the areabetween orifice 6a of inner nozzle 6 and orifice 7a' of outer nozzle 7.The inner wall surface 22 of the taper portion 21 of the outer nozzle 7when pressure is applied to molten glass 2 forces the molten glass 2 tosqueeze through a fine gap formed between the outer edge of orifice 6a,i.e. the outer edge of inner nozzle 6, and the inner surface 22 to formthe thin molten glass film 9' across orifice 6a and 7a'. Thus, theformation of the molten film 9' does not in this embodiment rely solelyon the surface tension properties or the molten glass. The illustratedcoaxial nozzle can be used to produce microspheres having diametersthree to five times the size of the diameter of orifice 7a of coaxialnozzle 7 and allows making microspheres of smaller diameter than thosemade using the FIG. 2 apparatus and is particularly useful in blowinghigh viscosity glass materials.

The diameter of the microsphere is determined by the diameter of orifice7a'. This apparatus allows the use of larger inner diameters of outernozzle 7 and larger inner diameters of inner nozzle 6, both of whichreduce the possibility of plugging of the coaxial nozzles when in use.These features are particularly advantageous when the blowing gascontains dispersed metal particles and/or the glass compositions containadditive material particles.

The FIGS. 3a and 3b of the drawings illustrate another preferredembodiment of the invention in which the outer portion of the transversejet 13 is flattened to form a generally rectangular or oval shapedorifice opening 13a. The orifice opening 13a can be disposed at an anglerelative to a line drawn through the central axis of coaxial nozzle 5.The preferred angle, however, is that as illustrated in the drawing.That is, at an angle of about 90° to the central axis of the coaxialnozzle 5.

The use of the flattened transverse jet entraining fluid was found, at agiven velocity, to concentrate the effect of the fluctuating pressurefield and to increase the amplitude of the pressure fluctuations inducedin the region of the formation of the hollow microspheres at theopposite or lee side of the blowing nozzle 5. By the use of theflattened transverse jet and increasing the amplitude of the pressurefluctuations, the pinching action exerted on the cylinder 12 isincreased. This action facilitates the closing off of the cylinder 12 atits inner pinched end 16 and detaching of the cylinder 13 from theorifice 7a of the center nozzle 7.

The FIG. 3c of the drawings illustrates another preferred embodiment ofthe present invention in which a high viscosity glass material is usedto blow hollow glass filamented microspheres. In this Figure, theelongated shaped cylinder 12 and glass microspheres 17a, 17b and 17c areconnected to each other by thin glass filaments 17d. As can be seen inthe drawing, as the microspheres 17a, 17b and 17c progress away fromblowing nozzle 5 surface tension forces act on the elongated cylinder 12to effect the gradual change of the elongated shaped cylinder 12 to thegenerally spherical shape 17a, more spherical shape 17b and finally thespherical shape microsphere 17c. The same surface tension forces cause agradual reduction in the diameter of the connecting filaments 17d, asthe distance between the microspheres and filaments and the blowingnozzle 5 increases. The hollow glass microspheres 17a, 17b and 17c thatare obtained are connected by thin filament portions 17d that aresubstantially of equal length and that are continuous with the glassmicrosphere.

The operation of the apparatus illustrated in FIGS. 3, 3a, 3b and 3c issimilar to that discussed above with regard to FIGS. 1 and 2 of thedrawings.

The FIG. 4 of the drawings illustrates an embodiment of the invention inwhich the lower portion of the coaxial nozzle 7 is provided with abulbous member 23 which imparts to the outer nozzle 7 a spherical shape.This embodiment as in the previous embodiments comprises coaxial blowingnozzle 5 which consists of inner nozzle 6 with orifice 6a and outernozzle 7 with orifice 7a. The figure of the drawings also showselongated cylinder shaped liquid film 12 with the pinched portion 16.

The use of the bulbous spherical shaped member 23 was found for a givenvelocity of entraining fluid 14 (FIG. 2) to substantially increase theamplitude of the pressure fluctuations induced in the region of theformation of the hollow mircospheres at the opposite or lee side of theblowing nozzle 5. By the use of the bulbous member 23 and increasing theamplitude of the pressure fluctuations, the pinching action exerted onthe elongated cylinder 12 is increased. This action facilitates theclosing off of the cylinder 12 at its inner pinched end 16 and detachingthe cylinder 12 from the orifice 7a of the outer nozzle 7.

In still another embodiment of the invention which is also illustratedin FIG. 4 of the drawings, a beater bar 24 can be used to assist indetaching the cylinder 12 from orifice 7a. The beater bar 24 is attachedto a spindle, not shown, which is caused to rotate in a manner such thatthe beater bar 24 is brought to bear upon the pinched portion 16 of theelongated cylinder 12 and to thus facilitate the closing off of thecylinder 12 at its inner pinched end 16 and detaching the cylinder 12from the orifice 7a of outer nozzle 7.

The operation of the apparatus illustrated is otherwise similar to thatdisclosed above with regard to FIGS. 1, 2, 3 and 4.

The embodiments of the invention illustrated in the FIGS. 2 to 4 can beused singly or in various combinations as the situation may require. Theentire apparatus can be enclosed in a high pressure containment vessel,not shown, which allows the process to be carried out at elevatedpressures.

The FIG. 5 of the drawings illustrates the use of the hollow glassmicrospheres of the present invention in the construction of a flatplate solar energy collector 29. The drawing shows a cross-section takenfrom an end view of the solar collector. The outer cover member 30protects the solar collector from the weather elements. The cover member30 can be made from clear glass or plastic. The cover member 30 can alsobe made from several layers of transparent hollow glass vacuummicrospheres of this invention bonded together with a transparentpolyester, polyolefin, polyacrylate or polymethyl acrylate resin to forma transparent cover. There is disposed below and parallel to cover 30 ablack coated flat metal plate absorber 31 to which there is bonded tothe bottom surface thereof a multiplicity of evenly spaced heat exchangemedium 32 containing tubes 33. The heat exchange medium can, forexample, be water and the tubes 33 are interconnected by conventionalmeans not shown to allow for the flow of the heat exchange medium 32through the tubes 33. In order to minimize heat loss from the solarcollector and increase its efficiency, the space between the outer cover30 and the flat plate absorber 31 can be filled with a bed oftransparent hollow glass vacuum microspheres 34 of the presentinvention. The solar collector 29 has an inner cover member 35 by meansof which the collector can be attached to a roof 36 of a home. Tofurther decrease the heat loss of the solar collector and increase itsefficiency, the space between the lower surface of the flat plateabsorber 31 and the inner cover member 35 can be filled with reflectivehollow glass vacuum microspheres 39 containing on the inner surfacethereof a highly reflective metal coating. The end members 37 and 38 ofthe solar collector 29 close-off the top and bottom edges of thecollector.

The construction and operation of the flat plate solar collector areotherwise essentially the same as the known flat plate solar collectors.

The FIG. 6 of the drawings illustrates the use of the hollow glassmicrospheres of the present invention in the construction of a tubularsolar energy collector 43. The drawing shows a cross-section taken froman end view of the solar collector. The outer cover member 44 can bemade from clear glass or plastic. The cover member 44 can also be madefrom several layers of light transparent hollow glass vacuummicrospheres of this invention bonded together with a transparentpolyester or polyolefin resin to form a transparent cover. There isdisposed below and parallel to cover 30 a double pipe tubular member 45.The tubular member 45 consists of an inner feed tube 46 and an outerreturn tube 47. The heat exchange medium 48, for example water, is fedthrough inner feed tube 46, passes to one end of the tube where itreverses its direction of flow, by means not shown, and the heatexchange medium 49 (return) passes back through the return tube 47. Theinner feed tube 46 is coaxial to the outer return tube 47. The outerreturn tube 47 has on its surface a black heat absorbing coating. Theheat exchange medium in passing through feed tube 46 and return tube 47is heated.

The tubular collector 43 has outer parallel side covers 50 and a lowerouter curved cover portion 51. The lower curved cover portion 51 isconcentric with the inner tube 46 and outer tube 47. The inner surfaceof the lower portion 51 is coated with a reflecting material 52 suchthat the sun's rays are reflected and concentrated in the direction ofthe black heat absorbing surface coating of return tube 47. In order tominimize heat loss from the solar collector and increase its efficiency,the entire area between the outer covers 44, 50 and 51 and the returntube 47 can be filled with a bed of the light transparent hollow glassvacuum microspheres 54 of the present invention.

The tubular solar collector 42 is normally mounted in groups in a mannersuch that they intercept the movement of the sun across the sky. Thesun's rays pass through the transparent microspheres 54 and impingeddirectly on the outer side of the return tube 47 and are reflected byreflector 52 and impinged on the lower inner side of return tube 47.

The construction and operation of the tubular solar collector areotherwise essentially the same as the known tubular solar collectors.

The FIG. 7 of the drawings illustrates the use of the hollow glassmicrospheres of the present invention in the construction of a formedpanel 61. The panel contains multiple layers of uniform sized glassmicrospheres 62. The microspheres can have a thin deposited layer 63 ofa reflecting metal deposited on their inner wall surface. The internalvolume of the microspheres can contain a high vacuum or can be filledwith a low heat conductivity gas 64 and the interstices 65 between themicrospheres can be filled with the same gas or a low heat conductivityfoam containing a low heat conductivity gas. The facing surface 66 canbe coated with a thin layer of plaster suitable for subsequent sizingand painting and/or covering with wall paper. The backing surface 67 canbe coated with the same or different plastic to form a vapor barrier orwith plaster or with both materials.

The FIG. 7a of the drawings illustrates the use of the hollow glassmicrospheres of the present invention in the construction of a formedpanel 71. The panel contains multiple layers of uniform sized flattenedoblate spheriod shaped microspheres 72. The oblate spheriod shapedmicrospheres can have an inner thin deposited layer 73 of a reflectivemetal. The internal volume of the microsphere can contain a high vacuumor can be filled with a low heat conductivity gas 74. The flattenedconfiguration of the microspheres substantially reduces the volume ofthe interstices between the microspheres which can be filled with a lowheat conductivity foam 75 containing a low heat conductivity gas. Thefacing 76 can be coated with a thin layer of plaster suitable forsubsequent sizing and painting and/or covering with wall paper. Thebacking surface 77 can be coated with a suitable plastic to form a vaporbarrier or with plaster or with both materials.

The FIG. 7b of the drawings illustrates an embodiment of the formed wallpanel of FIG. 7a in which filamented hollow glass microspheres connectedby very thin glass filaments 78 are used. The thin glass filaments 78are formed between adjacent microspheres when and as the microspheresare blown and join the microspheres together by continuous glassmaterial. The connecting filaments 78 in the formed panel interrupt thewall to wall contact between the microspheres and serve to substantiallyreduce the conduction heat transfer between adjacent microspheres. Theuse of filamented microspheres to provide the interrupting filaments isparticularly advantageous and preferred because the filaments arepositively evenly distributed, cannot settle, are supplied in thedesired controlled amount, and in the formed panel provide aninterlocking structure which serves to strengthen the formed panel. Thefacing 76, as before, can be coated with a thin layer of plastersuitable for subsequent sizing and painting and/or covering with wallpaper. The backing surface 77 can be coated with a suitable plastic toform a vapor barrier or with plaster or with both materials.

The FIG. 8 of the drawings illustrates in graphic form the relationshipbetween the thickness of the thin metal film deposited on the inner wallsurface of the hollow microsphere, the metal vapor blowing gas pressureand the inner diameter of the microspheres. A preferred metal vaporblowing gas is zinc vapor.

INORGANIC FILM FORMING MATERIAL AND GLASS COMPOSITIONS

The inorganic film forming material and compositions and particularlythe glass compositions from which the hollow glass microspheres of thepresent invention are made can be widely varied to obtain the desiredphysical characteristics for heating, blowing, forming, cooling andhardening the microspheres and the desired heat insulating, strength,gas permeability and light transmission characteristics of the glassmicrospheres produced.

The glass compositions can be selected to have a low heat conductivityand sufficient strength when cooled and solidified to, when themicrosphere contains a high vacuum, withstand atmospheric pressure. Themolten glass composition forms hard microspheres which are capable ofcontacting adjacent microspheres without significant wear ordeterioration at the points of contact and are resistant todeterioration from exposure to moisture, heat and/or weathering.

The constituents of the glass compositions can vary widely, depending ontheir intended use, and can include naturally occurring andsynthetically produced glass materials.

The constituents of the glass compositions can be selected and blendedto have high resistance to corrosive gaseous materials, high resistanceto gaseous chemical agents, high resistance to alkali and weather, lowsusceptibility to diffusion of gaseous materials into and out of theglass microspheres, and to be substantially free of trapped gas bubblesor dissolved gases in the walls of the microspheres which can formbubbles and to have sufficient strength when cured, hardened andsolidified to support a substantial amount of weight and/or withstand asubstantial amount of pressure.

The microspheres of the present invention a capable of contactingadjacent microspheres without significant wear or deterioration at thepoints of contact and are resistant to deterioration from exposure tomoisture, heat and/or weathering.

The glass compositions preferably contain relatively large amounts ofsilicon dioxide, alumina, lithium, zirconia, and lime and relativelysmall amounts of soda. Calcium can be added to assist in melting theglass and boric oxide can be added to improve the weathering propertiesof the glass. The glass compositions are formulated to have relativelyhigh melting and fluid flow temperatures with a relatively narrowtemperature difference between the melting i.e. fluid flow and hardeningtemperatures. The glass compositions are formulated such that they havea high rate of viscosity increase with decreasing temperature so thatthe microsphere walls will solidify, harden and strengthen before theblowing gas within the sphere decreases in volume and pressure asufficient amount to cause the microsphere to collapse. Where it isdesirous to maintain positive pressure or a high vacuum in the innervolume of the microspheres, the permeability to gases such as heliumrequires reduction of the network formers, such as silica, and theinclusion of network modifiers, such as alumina. Other means fordecreasing the permeability of the hollow glass microspheres to gasesare discussed below.

The glass compositions suitable for use in the present invention canhave the range of proportions listed below in Columns A, B and C, inpercent by weight.

                  TABLE 1                                                         ______________________________________                                                A         B          C                                                        (Alumina) (Lithium)  (Zirconia)                                       ______________________________________                                        SiO.sub.2 46-64       58-85      40-58                                        Al.sub.2 O.sub.3                                                                        10-22       0-25       6-12                                         Li.sub.2 O                                                                              --          8-25       --                                           Zirconia  --          --         8-20                                         CaO       5-18        0-2        1-3                                          MgO       0-12        0-2        0-4                                          B.sub.2 O.sub.3                                                                         4-12        2-6        0-6                                          Na.sub.2 O                                                                              0-1         0-1.0      0-2.5                                        BaO       0-2.0       0-2.0      0-2.0                                        CaF.sub.2 0-2.0       0-2.0      0-2.0                                        K.sub.2 O 0-0.7       0-0.7      0.5-1.5                                      ______________________________________                                    

The compositions of Columns A and B do not contain zirconia whereas thecompositions of Column C are relatively high in zirconia content.

The use of glass compositions containing a relatively high aluminacontent and a relatively low soda content was found to produce a rapidhardening of the glass microspheres, which facilitated the production ofglass microspheres and in particular glass microspheres having a highcontained vacuum.

The Table 2 below shows in Column I a high alumina content glasscomposition of the present invention and in Column II a high sodacontent glass composition heretofore used to make glass microspheres.

The glass microspheres made from the Columns I and II glass compositionare made in accordance with the present invention by blowing the glasswith an inert blowing gas.

                  TABLE 2                                                         ______________________________________                                                     I       II                                                                    (Alumina)                                                                             (Soda)                                                   ______________________________________                                        SiO.sub.2      57.0      72.2                                                 Al.sub.2 O.sub.3                                                                             20.5      1.2                                                  CaO            5.5       8.8                                                  MgO            12        3.3                                                  B.sub.2 O.sub.3                                                                              4         --                                                   Na.sub.2 O     1.0       14.2                                                 ______________________________________                                    

The Table 3 below compares the increase in viscosity on cooling of thehigh alumina content (I) and the high soda content (II) glasscompositions of Table 2.

                  TABLE 3                                                         ______________________________________                                                     Temperature                                                                              Viscosity-Poises                                      ______________________________________                                        High Alumina Comp.                                                                           2700° F.                                                                            30                                                (I)            1830° F.                                                                            10 × 10.sup.5                                              1470° F.                                                                            10 × 10.sup.10                              High Soda Comp.                                                                              2700° F.                                                                            100                                               (II)           1830° F.                                                                            10 × 10.sup.3                                              1470° F.                                                                            10 × 10.sup.5                               ______________________________________                                    

The Table 3 shows that the high alumina content glass has asubstantially faster hardening rate than the high soda content glasssuch that in the first 1300° F. of chilling, the high alumina contentglass had a viscosity of 10×10⁵ times greater than that of the high sodacontent glass.

For certain uses relatively low temperature melting glass compositionscan be used. The low melting glass compositions can contain relativelylarge amounts of lead. Naturally occurring glass materials such asbasaltic mineral compositions can also be used. The use of thesenaturally occurring glass compositions can in some cases substantiallyreduce the cost of the raw materials used.

Suitable lead containing glass compositions and basaltic mineralcompositions are in Table 4.

                  TABLE 4                                                         ______________________________________                                                    D     E                                                                       (Lead)                                                                              (Basalt)*                                                   ______________________________________                                        SiO.sub.2     30-70   40-55                                                   Al.sub.2 O.sub.3                                                                            0-2     13-17                                                   Pb            10-60   --                                                      Fe.sub.2 O.sub.3                                                                            --      2-16                                                    FeO           --      1-12                                                    CaO           0-5     7-14                                                    MgO           0-3     4-12                                                    Na.sub.2 O    0-9     2-4                                                     K.sub.2 O     0-9     1-2                                                     H.sub.2 O     --      0.5-4                                                   TiO.sub.2     --      0.5-4                                                   ______________________________________                                         *See G. L. Sheldon, Forming Fibres from Basalt Rock, Platinum Metals          Review, pages 18 to 34, 1978.                                            

The discussions in the present application with respect to glasscompositions is applicable to the various glass compositions mentionedincluding the naturally occurring basaltic mineral compositions.

There may be added to the glass compositions chemical agents whicheffect the viscosity of the compositions in order to obtain the desiredviscosities for blowing the microspheres.

To assist in the blowing and formation of the glass microspheres and theglass vacuum microspheres and to control the surface tension andviscosity of the spheres suitable surface active agents, such ascolloidal particles of insoluble substances and viscosity stabilizerscan be added to the glass composition as additives. A distinct andadvantageous feature of the present invention is that latent solid orlatent liquid blowing gases are not used or required and that themicrospheres that are produced are free of latent solid or latent liquidblowing gas materials or gases.

The glass compositions from which the hollow glass microspheres can bemade are, depending on the particular glass materials used, to somedegree permeable to the gas materials used to blow the microspheresand/or to the gases present in the medium surrounding the microspheres.The gas permeability of the glass compositions can be controlled,modified and/or reduced or substantially eliminated by the addition,prior to blowing the microspheres, to the glass composition of verysmall inert laminar plane-orientable additive material particles. Whenany one or more of these laminar plane-orientable additive materialparticles are added to a glass composition prior to the blowing andformation of the hollow glass microsphere, the process of making themicrosphere aligns the laminar particles, as the glass film is stretchedin passing, i.e. extruded, through the conical blowing nozzle, with thewalls of the hollow glass microsphere and normal to the gas diffusiondirection. The presence of the laminar plane particles in themicrosphere walls substantially diminishes the gas permeability of theglass film. The sizes of the additive particles are advantageouslyselected to be less than one-half the thickness of the wall of themicrospheres.

BLOWING GAS

The hollow microspheres and particularly the glass microspheres can beblown with a gas, an inert gas, an inert metal vapor or gas containingdispersed metal particles or mixtures thereof. The microspheres can beused to make insulating materials and/or filler materials.

The inert gases used to blow the microspheres are selected to have a lowheat conductivity and generally involve heavy molecules which do nottransfer heat readily. Suitable blowing gases are argon, xenon, carbondioxide, nitrogen, nitrogen dioxide, sulfur and sulfur dioxide. Organometal compounds can also be used as a blowing gas. The blowing gas isselected to have the desired internal pressure when cooled to ambienttemperatures. When sulfur, for example, is used as a blowing gas, thesulfur condenses and a partial vacuum can be formed in the microsphere.

Blowing gases can also be selected that react with the inorganic filmforming material or composition, e.g. the glass microspheres, forexample, to assist in the hardening of the microspheres or to make themicrosphere less permeable to the contained blowing gases. The blowinggases can also be selected to react with the deposited thin metal layerto obtain desired characteristics in the metal layer. For example, toreduce the thermal conductivity of the metal layer.

For certain uses, oxygen or air can be used as or added to the blowinggas.

The metal vapor is used as a blowing gas to obtain a substantial vacuumin the contained volume of the microsphere and to deposit a thin metalcoating on the inner wall surface of the hollow glass microsphere. Thespecific metal used as well as the thickness and nature of metal coatingdeposited will determine whether the metal coating is transparent orreflective of visible light.

The metal vapor used to blow the hollow glass microspheres is selectedto have the desired vaporization temperature, latent heat capacity andvapor pressure at the blowing temperature, and to have the desired vaporpressure at the solidification temperature and ambient temperature. Thecondensing and depositing of the metal vapor within the hollow glassmicrosphere produces a vapor pressure equivalent to the vapor pressureof the metal at room temperature, i.e. about zero vapor pressure. Thethickness of the deposited metal coating will depend to some extent uponthe metal vapor pressure used to blow the microsphere, the size of themicrosphere and the temperature of the molten glass.

Small amounts of metal vapors, e.g. alkali metals, that act as getteringmaterials can be added to the metal vapor blowing gas. The getteringmaterials react with gases evolved from the molten glass film during theformation of the microspheres and maintain the hard contained vacuum.

The metal vapor blowing gases such as zinc, antimony, barium, cadmium,cesium, bismuth, selenium, lithium, magnesium, and potassium can beused. Zinc and selenium, however, are preferred and zinc is particularlypreferred.

An auxilliary blowing gas, e.g. an inert blowing gas can advantageouslybe used in combination with a metal vapor blowing gas to assist in thecontrol of the cooling and solidification of the hollow molten glassmicrosphere. The auxilliary blowing gas accomplishes this purpose bymaintaining the partial pressure of the auxilliary blowing gas in themicrosphere for a sufficient period of time to allow the molten glassmicrosphere to solidify, harden and strengthen while the metal vapor isbeing condensed and the metal vapor pressure is substantially reduced.That is, the pressure drop of the blowing gas is slowed and a slightlylower vacuum is formed in the microsphere.

A blowing gas containing dispersed metal particles can be used to obtainin the contained volume of the microsphere a deposit of a thin metalcoating on the inner wall surface of the hollow glass microsphere. Thethickness of metal coating deposited will determine whether the metalcoating is transparent or reflective of visible light.

The metal used to coat the inner wall surface of the hollow glassmicrospheres is selected to have the desired emissivity, low heatconduction characteristics, and to adhere to the inner wall surface ofthe glass microspheres. The thickness of the deposited metal coatingwill depend to some extent upon the metal, the particle size of themetal used, the size of the microspheres and the amount of dispersedmetal particles used.

The dispersed metal particle size can be 25 A to 10,000 A, preferably 50A to 5,000 A and more preferable 100 A to 1,000 A. A sufficient amountof the metal is dispersed in the blowing gas to obtain the desiredthickness of the deposited metal. The dispersed metal particles canadvantageously be provided with an electrostatic charge to assist indepositing them on the inner wall surface of the microspheres.

Metal particles such as aluminum, silver, nickel, zinc, antimony,barium, cadmium, cesium, bismuth, selenium, lithium, magnesium,potassium, and gold can be used. Aluminum, zinc and nickel, however, arepreferred. Dispersed metal oxide particles can in a similar manner beused to obtain similar effects to that of the metals. In addition, themetal oxide particles can be used to produce a deposited film of lowerheat conductivity characteristics.

The thin metal coating can also be deposited on the inner wall surfaceof the microsphere by using as or with blowing gas organo metalcompounds that are gases at the blowing temperatures. Of the organometal compounds available, the organo carbonyl compounds are preferred.Suitable organo metal carbonyl compounds are nickel and iron.

The organo metal compounds can be decomposed by heating just prior toblowing the microspheres to obtain finely dispersed metal particles anda decomposition gas. The decomposition gas, if present, can be used toassist in blowing the microspheres. The dispersed metal particles fromdecomposition of the organo metal compound, as before, deposit to formthe thin metal layer. Alternatively, the microsphere, after being formedand containing the gaseous organo metal compound blowing gas, can besubjected to an "electric discharge" means which decomposes the organometal compound to form the finely dispersed metal particles and thedecomposition gas.

The thickness of the deposited metal layer will depend primarily on thepartial pressure of the gaseous organo metal blowing gas and the insidediameter of the microsphere.

An auxiliary blowing gas can be used to dilute the gaseous organo metalcompound blowing gas in order to control the thickness of the depositedmetal layer. There can also be used as an auxiliary blowing gas, a gasthat acts as a catalyst for the decomposition of the organo metalcompound or as a hardening agent for the glass compositions. Theaddition of the catalyst or hardening agent to the blowing gas preventscontact of the catalyst with the organo metal compound or the hardeningagent with the glass composition until a time just before themicrosphere is formed.

The entraining fluid can be a gas at a high or low temperature and canbe selected to react with or be inert to the glass composition. Theentraining fluid, e.g. an inert entraining fluid, can be a hightemperature gas. Suitable entraining fluids are nitrogen, air, steam andargon.

An important feature of the present invention is the use of thetransverse jet to direct the inert entraining fluid over and around thecoaxial blowing nozzle. The entraining fluid assists in the formationand detaching of the hollow molten glass microsphere from the coaxialblowing nozzle.

The quench fluid can be a liquid, a liquid dispersion or a gas. Suitablequench fluids are steam, a fine water spray, air, nitrogen or mixturesthereof.

The inert quench fluid can be ethylene glycol vapor or liquid, steam, afine water spray, or mixtures thereof. The hollow molten glassmicrospheres immediately after they are formed are rapidly quenched andcooled to solidify, harden and strengthen the glass microspheres beforethe internal gas pressure is reduced to such a low value that themicrosphere collapses. The selection of a specific quench fluid andquench temperature depends to some extent on the glass composition fromwhich the microsphere was formed and on the blowing gas or metal vaporused to blow the microsphere and on the metal and nature of thedeposited metal film desired.

PROCESS CONDITIONS

The inorganic film forming materials and/or compositions of the presentinvention are heated to a temperature of about 1800° to 3100° F. andmaintained in a liquid, fluid form at the desired blowing temperatureduring the blowing operation. The glass composition is heated to atemperature of 2000° to 2800° F., preferably 2300° to 2750° F. and morepreferably 2400° to 2700° F., depending on the constituents of thecomposition. The lead containing glass compositions can be heated to atemperature of, for example, about 1800° to 2900° F. The basalticmineral glass compositions can be heated to a temperature of, forexample, about 2100° to 3100° F.

The glass compositions at these temperatures, i.e. the blowingtemperatures, is molten, fluid and flows easily. The molten glass justprior to the blowing operation has a viscosity of 10 to 600 poises,preferably 20 to 350, and more preferably 30 to 200 poises. The moltenlead containing glass compositions just prior to the blowing operationhave a viscosity of, for example, 10 to 500 poises. The molten basalticmineral glass composition just prior to the blowing operation can have aviscosity of, for example, 15 to 400 poises.

Where the process is used to make non-filamented microspheres, theliquid glass just prior to the blowing operation can have a viscosity of10 to 200 poises, preferably 20 to 100 poises, and more preferably 25 to75 poises.

Where the process is used to make filamented microspheres, the liquidglass just prior to the blowing operation can have a viscosity of 50 to600 poises, preferably 100 to 400 poises, and more preferably 150 to 300poises.

A critical feature of the present invention is that the formation of thehollow glass microspheres can be carried out at low viscosities relativeto the viscosities heretofore used in the prior art processes thatutilized latent liquid or solid blowing agents dispersed throughout orcontained in the glass compositions used to blow the microspheres.Because of the ability to utilize comparatively low viscosities,applicant is able to obtain hollow glass microspheres, the wall of whichare free of any entrapped or dissolved gases or bubbles. With the lowviscosities used by applicant, any entrapped or dissolved gases diffuseout and escape from the glass film surface during the bubble formation.With the high viscosities required to be used in the prior artprocesses, any dissolved gases are trapped in the walls of the glassmicrospheres as they are formed because of the high viscosities requiredto be used.

The glass during the blowing operation exhibits a surface tension of 150to 400 dynes/cm, preferably 200 to 350 dynes/cm and more preferably 250to 325 dynes/cm.

The molten or liquid glass fed to the coaxial blowing nozzle can be atabout ambient pressure or can be at an elevated pressure. The molten orliquid glass feed can be at a pressure of 1 to 20,000 p.s.i.g., usually3 to 10,000 p.s.i.g. and more usually 5 to 5,000 p.s.i.g. The moltenglass feed when used for low pressure applications can be at a pressureof 1 to 1000 p.s.i.g., preferably 3 to 500 p.s.i.g. and more preferably5 to 100 p.s.i.g. p Where the process is used to make microspheres foruse as insulating materials and in insulating systems, for use insyntactic foam systems and as filler materials in general, the liquidglass fed to the coaxial blowing nozzle can also be at a pressure of 1to 1,000 p.s.i.g., preferably at 3 to 100 p.s.i.g., and more preferablyat 5 to 50 p.s.i.g.

The molten glass is continuously fed to the coaxial blowing nozzleduring the blowing operation to prevent premature breaking and detachingof the elongated cylinder shaped molten glass liquid film as it is beingformed by the blowing gas.

The blowing gas, inert blowing gas, gaseous material blowing gas ormetal vapor will be at about the same temperature as the molten glassbeing blown. The blowing gas temperature can, however, be at a highertemperature than the molten glass to assist in maintaining the fluidityof the hollow molten glass microsphere during the blowing operation orcan be at a lower temperature than the molten glass to assist in thesolidification and hardening of the hollow molten glass microsphere asit is formed. The pressure of the blowing gas is sufficient to blow themicrosphere and will be slightly above the pressure of molten glass atthe orifice 7a of the outer nozzle 7. The blowing gas pressure will alsodepend on and be slightly above the ambient pressure external to theblowing nozzle.

The temperatures of the blowing gases will depend on the blowing gasused and the viscosity-temperature-shear relationship for the glassmaterials used to make the microspheres.

The metal vapor blowing gas temperature will be sufficient to vaporizethe metal and will be at about the same temperature as the molten glassbeing blown. The metal vapor blowing gas temperature can, however, be ata higher temperature than the molten glass to assist in maintaining thefluidity of the hollow molten glass microsphere during the blowingoperation or can be at a lower temperature than the molten glass toassist in the solidification and hardening of the hollow molten glassmicrosphere as it is formed. The pressure of the metal vapor blowing gasis sufficient to blow the microsphere and will be slightly above thepressure of molten glass at the orifice 7a of the outer nozzle 7. Themetal vapor blowing gas pressure will also depend on and be slightlyabove the ambient pressure external to the blowing nozzle.

The pressure of the blowing gas or gaseous material blowing gas,including the metal vapor blowing gas, is sufficient to blow themicrosphere and will be slightly above the pressure of liquid glass atthe orifice 7a of the outer nozzle 7. Depending on the gaseous materialto be encapsulated within the hollow glass microspheres, the blowing gasor the gaseous material can be at a pressure of 1 to 20,000 p.s.i.g.,usually 3 to 10,000 p.s.i.g. and more usually 5 to 5,000 p.s.i.g.

The blowing gas or gaseous material blowing gas can also be at apressure of 1 to 1,000 p.s.i.g., preferably 3 to 500 p.s.i.g. and morepreferably 5 to 100 p.s.i.g.

Where the process is used to make microspheres for use as insulatingmaterials and in insulating systems, for use in syntactic foam systemsand as filler materials in general, the blowing gas or gaseous materialblowing gas can be at a pressure of 1 to 1,000 p.s.i.g., preferably at 3to 100 p.s.i.g. and more preferably at 5 to 50 p.s.i.g.

The pressure of the blowing gas containing dispersed metal particlesalone and/or in combination with the principle blowing gas is sufficientto blow the microsphere and the combined gas pressure will be slightlyabove the pressure of the liquid glass at the orifice 7a of the outernozzle 7. The pressure of the combined mixture of the blowing gases willalso depend on and be slightly above the ambient pressure external tothe blowing nozzle.

The ambient pressure external to the blowing nozzle can be at aboutatmospheric pressure or can be at subatmospheric or super-atmosphericpressure. Where it is desired to have a relatively or high pressure ofcontained gas in the microsphere or to deposit a relatively thickcoating of metal within a vacuum microsphere, the ambient pressureexternal to the blowing nozzle is maintained at a super-atmosphericpressure. The ambient pressure external to the blowing nozzle will, inany event, be such that it substantially balances, but is slightly lessthan the blowing gas pressure.

The transverse jet inert entraining fluid which is directed over andaround the coaxial blowing nozzle to assist in the formation anddetaching of the hollow molten glass microsphere from the coaxialblowing nozzle can be at about the temperature of the molten glass beingblown. The entraining fluid can, however, be at a higher temperaturethan the molten glass to assist in maintaining the fluidity of thehollow molten glass microsphere during the blowing operation or can beat a lower temperature than the molten glass to assist in thestabilization of the forming film and the solidification and hardeningof the hollow molten glass microsphere as it is formed.

The transverse jet entraining fluid which is directed over and aroundthe coaxial blowing nozzle to assist in the formation and detaching ofthe hollow liquid glass microsphere from the coaxial blowing nozzle canhave a linear velocity in the region of microsphere formation of 1 to120 ft/sec, usually 5 to 80 ft/sec and more usually 10 to 60 ft/sec.

Where the process if used to make non-filamented microspheres, thelinear velocity of the transverse jet fluid in the region of microsphereformation can be 30 to 120 ft/sec, preferably 40 to 100 ft/sec and morepreferably 50 to 80 ft/sec.

Where the process is used to make filamented microspheres, the linearvelocity of the transverse jet fluid in the region of microsphereformation can be 1 to 50 ft/sec, preferably 5 to 40 ft/sec and morepreferably 10 to 30 ft/sec.

Further, it is found (FIGS. 2 to 4) that pulsing the transverse jetentraining fluid at a rate of 2 to 1500 pulses/sec, preferably 50 to1000 pulses/sec and more preferably 100 to 500 pulses/sec assist incontrolling the diameter of the microspheres and the length of thefilament portion of the filamented microspheres and detaching themicrospheres from the coaxial blowing nozzle.

The distance between filamented microspheres depends to some extent onthe viscosity of the glass and the linear velocity of the transverse jetentraining fluid.

The entraining fluid can be at the same temperature as the liquid glassbeing blown. The entraining fluid can, however, be at a highertemperature than the liquid glass to assist in maintaining the fluidityof the hollow liquid glass microsphere during the blowing operation orcan be at a lower temperature than the liquid glass to assist in thestabilization of the forming film and the solidification and hardeningof the hollow liquid glass microsphere as it is formed.

The quench fluid is at a temperature such that it rapidly cools thehollow molten glass microsphere to solidify, harden and strengthen themolten glass before the inner gas pressure or metal vapor pressuredecreases to a value at which the glass microsphere would collapse. Thequench fluid can be at a temperature of 0 to 200° F., preferably 40° to200° F. and more preferably 50° to 100° F. depending to some extent onthe glass composition.

The quench fluid very rapidly cools the outer molten glass surface ofthe microsphere with which it is in direct contact and more slowly coolsthe blowing gas or metal vapor enclosed within the microsphere becauseof the lower thermal conductivity of the gas or vapor. This coolingprocess allows sufficient time for the glass walls of the microspheresto strengthen before the gas is cooled or the metal vapor is cooled andcondensed and a high vacuum formed within the glass microsphere.

The cooling and deposition of the metal vapor on the inner wall surfaceof the microspheres can be controlled to optimize the crystal size ofthe metal deposited such that sufficiently large crystals are obtainedthat the deposited metal film is discontinuous. The discontinuities inthe metal film reduce the thermal conductivity of the metal film whileat the same time retaining the metal films ability to reflect radiantheat.

The time elapsed from commencement of the blowing of the glassmicrospheres to the cooling and hardening of the microspheres can be0.0001 to 1.0 second, preferably 0.0010 to 0.50 second and morepreferably 0.010 to 0.10 second.

The filamented microsphere embodiment of the invention provides a meansby which the microspheres may be suspended and allowed to harden andstrengthen without being brought into contact with any surface. Thefilamented microspheres are simply drawn on a blanket or drum and aresuspended between the blowing nozzle and the blanket or drum for asufficient period of time for them to harden and strengthen.

APPARATUS

Referring to FIGS. 1 and 2 of the drawings, the refractory vessel 1 isconstructed to maintain the molten glass at the desired operatingtemperatures. The molten glass 2 is fed to coaxial blowing nozzle 5. Thecoaxial blowing nozzle 5 consists of an inner nozzle 6 having an outsidediameter of 0.32 to 0.010 inch, preferably 0.20 to 0.015 inch and morepreferably 0.10 to 0.020 inch and an outer nozzle 7 having an insidediameter of 0.420 to 0.020 inch, preferably 0.260 to 0.025 and morepreferably 0.130 to 0.030 inch. The inner nozzle 6 and outer nozzle 7form annular space 8 which provides a flow path through which the moltenglass 2 is extruded. The distance between the inner nozzle 6 and outernozzle 7 can be 0.050 to 0.004, preferably 0.030 to 0.005 and morepreferably 0.015 to 0.008 inch.

The orifice 6a of inner nozzle 6 terminates a short distance above theplane of orifice 7a of outer nozzle 7. The orifice 6a can be spacedabove orifice 7a at a distance of 0.001 to 0.125 inch, preferably 0.002to 0.050 inch and more preferably 0.003 to 0.025 inch. The molten glass2 flows downwardly and is extruded through annular space 8 and fills thearea between orifice 6a and 7a. The surface tension forces in the moltenglass 2 form a thin liquid molten glass film 9 across orifice 6a and 7awhich has about the same or a smaller thickness as the distance oforifice 6a is spaced above orifice 7a. The orifices 6a and 7a can bemade from stainless steel, platinum alloys, or fused alumina. Thesurface tension forces in the liquid glass 2 form a thin liquid glassfilm 9 across orifices 6a and 7a which has about the same or a smallerthickness as the distance of orifice 6a is spaced above orifice 7a. Themolten glass film 9 can be 25 to 3175 microns, preferably 50 to 1270microns and more preferably 76 to 635 microns thick.

The FIG. 2 blowing nozzle can be used to blow molten glass at relativelylow viscosities, for example, of 10 to 60 poises, and to blow hollowglass microspheres of relatively thick wall size, for example, of 20 to100 microns or more.

A blowing gas, inert blowing gas, gaseous material blowing gas or metalvapor blowing gas is fed through inner coaxial nozzle 6 and brought intocontact with the inner surface of molten glass film 9. The inert blowinggas exerts a positive pressure on the molten glass film to blow anddistend the film outwardly and downwardly to form an elongated cylindershaped liquid film 12 of molten glass filled with the blowing gas 10.The elongated cylinder 12 is closed at its outer end and is connected toouter nozzle 7 at the peripheral edge of orifice 7a.

The transverse jet 13 is used to direct an inert entraining fluid 14through nozzle 13 and transverse jet nozzle orifice 13a at the coaxialblowing nozzle 5. The coaxial blowing nozzle 5 has an outer diameter of0.52 to 0.030 inch, preferably 0.36 to 0.035 inch and more preferably0.0140 to 0.040 inch.

The process of the present invention was found to be very sensitive tothe distance of the transverse jet 13 from the orifice 7a of outernozzle 7, the angle at which the transverse jet was directed at coaxialblowing nozzle 5 and the point at which a line drawn through the centeraxis of transverse jet 13 intersected with a line drawn through thecenter axis of coaxial nozzle 5. The transverse jet 13 is aligned todirect the flow of entraining fluid 14 over and around outer nozzle 7 inthe microsphere forming region of the orifice 7a. The orifice 13a oftransverse jet 13 is located a distance of 0.5 to 14 times, preferably 1to 10 times and more preferably 1.5 to 8 times and still more preferably1.5 to 4 times the outside diameter of coaxial blowing nozzle 5 awayfrom the point of intersect of a line drawn along the center axis oftransverse jet 13 and a line drawn along the center axis of coaxialblowing nozzle 5. The center axis of transverse jet 13 is aligned at anangle of 15° to 85°, preferably 25° to 75° and more preferably 35° to55° relative to the center axis of the coaxial blowing nozzle 5. Theorifice 13 a can be circular in shape and have an inside diameter of0.32 to 0.010 inch, preferably 0.20 to 0.015 inch and more preferably0.10 to 0.020 inch.

The line drawn through the center axis of transverse jet 13 intersectsthe line drawn through the center axis of coaxial blowing nozzle 5 at apoint above the orifice 7a of outer nozzle 7 which is 0.5 to 4 times,preferably 1.0 to 3.5 times and more preferably 2 to 3 times the outsidediameter of the coaxial blowing nozzle 5. The transverse jet entrainingfluid acts on the elongated shaped cylinder 12 to flap and pinch itclosed and to detach it from the orifice 7a of the outer nozzle 7 toallow the cylinder to fall free, i.e. be transported away from the outernozzle 7 by the entraining fluid.

The transverse jet entraining fluid as it passes over and around theblowing nozzle fluid dynamically induces a periodic pulsating orfluctuating pressure field at the opposite or lee side of the blowingnozzle in the wake or shadow of the coaxial blowing nozzle. A similarperiodic pulsating or fluctuating pressure field can be produced by apulsating sonic pressure field directed at the coaxial blowing nozzle.The entraining fluid assists in the formation and detaching of thehollow glass microsphere from the coaxial blowing nozzle. The use of thetransverse jet and entraining fluid in the manner described alsodiscourages wetting of the outer wall surface of the coaxial blowingnozzle 5 by the molten glass being blown. The wetting of the outer walldisrupts and interfers with blowing the microspheres.

The quench nozzles 18 are disposed below and on both sides of coaxialblowing nozzle 5 a sufficient distance apart to allow the microspheres17 to fall between the quench nozzles 18. The inside diameter of quenchnozzle orifice 18a can be 0.1 to 0.75 inch, preferably 0.2 to 0.6 inchand more preferably 0.3 to 0.5 inch. The quench nozzles 18 directcooling fluid 19 at and into contact with the molten glass microspheres17 at a velocity of 2 to 14, preferably 3 to 10 and more preferably 4 to8 ft/sec to rapidly cool and solidify the molten glass and form a hard,smooth hollow glass microsphere.

The FIG. 3 of the drawings illustrates a preferred embodiment of theinvention. It was found that in blowing molten glass compositions athigh viscosities that it was advantageous to immediately prior toblowing the molten glass to provide by extrusion a very thin moltenglass liquid film for blowing into the elongated cylinder shape liquidfilm 12. The thin molten glass liquid film 9' is provided by having thelower portion of the outer coaxial nozzle 7 tapered downwardly andinwardly at 21. The tapered portion 21 and inner wall surface 22 thereofcan be at an angle at 15° to 75°, preferably 30° to 60° and morepreferably about 45° relative to the center axis of coaxial blowingnozzle 5. The orifice 7a' can be 0.10 to 1.5 times, preferably 0.20 to1.1 times and more preferably 0.25 to 0.8 times the inner diameter oforifice 6a of inner nozzle 6.

The thickness of the molten glass liquid film 9' can be varied byadjusting the distance of orifice 6a of inner nozzle 6 above orifice 7aof outer nozzle 7 such that the distance between the peripheral edge oforifice 6a and the inner wall surface 22 of tapered nozzle 21 can bevaried. By controlling the distance between the peripheral edge oforifice 6a and the inner wall surface 22 of the tapered nozzle to form avery fine gap and by controlling the pressure applied to feed the moltenglass 2 through annular space 8 the molten glass 2 can be squeezed orextruded through the very fine gap to form a relatively thin moltenglass liquid film 9'.

The proper gap can best be determined by pressing the inner coaxialnozzle 6 downward with sufficient pressure to completely block-off theflow of glass, and to then very slowly raise the inner coaxial nozzle 6until a stable system is obtained, i.e. until the microspheres are beingformed.

The tapered nozzle construction illustrated in FIG. 3 is as mentionedabove the preferred embodiment of the invention. This embodiment can beused to blow glass compositions at relatively high viscosities as wellas to blow glass compositions at the relatively low viscosities referredto with regard to FIG. 2 of the drawings. The FIG. 3 embodiment of theinvention is of particular advantage in blowing the thin walledmicrospheres for use in or as insulating materials.

When blowing high or low viscosity glass compositions, it was found tobe advantageous to obtain the very thin molten glass fluid film and tocontinue during the blowing operation to supply molten glass to theelongated cylinder shaped liquid film as it was formed. Where a highpressure is used to squeeze, i.e. extruded, the molten glass through thevery thin gap, the pressure of the inert blowing gas or metal vapor isgenerally less than the molten glass feed pressure, but slightly abovethe pressure of the molten glass at the coaxial blowing nozzle.

The tapered nozzle configuration of FIG. 3 is also particularly usefulin aligning the laminar plane-orientable glass additive materials. Thepassage of the glass material through the fine or narrow gap serves toalign the additive materials with the walls of the microspheres as themicrospheres are being formed.

The FIGS. 3a and 3b of the drawings also illustrate a preferredembodiment of the invention in which the transverse jet 13 is flattenedto form a generally rectangular or oval shape. The orifice 13a can alsobe flattened to form a generally oval or rectangular shape. The width ofthe orifice can be 0.96 to 0.030 inch, preferably 0.60 to 0.045 inch andmore preferably 0.030 to 0.060 inch. The height of the orifice can be0.32 to 0.010 inch, preferably 0.20 to 0.015 inch and more preferably0.10 to 0.020 inch.

With reference to FIG. 3c of the drawings which illustrates anembodiment of the present invention in which a high viscosity glassmaterial or composition is used to blow filamented hollow glassmicrospheres, there is shown the formation of the uniform diametermicrospheres spaced about equal distances apart. The numbered items inthis drawing have the same meanings as discussed above with reference toFIGS. 1, 2, 3, 3a and 3b.

With reference to FIG. 4 of the drawings which illustrates anotherembodiment of the invention, it was found that in blowing the moltenglass to form the elongated cylinder shaped liquid film 12 that it wasadvantageous to increase the outer diameter of the lower portion coaxialblowing nozzle 5. One method of increasing the outer diameter of coaxialblowing nozzle 5 is by providing the lower portion of outer nozzle 7with a bulbous member 23 which imparts to the lower portion of outernozzle 7 a spherical shape. The use of the bulbous spherical shapedmember 23 is found for a given velocity of the entraining fluid (FIG. 2)to substantially increase the amplitude of the pressure fluctuationsinduced in the region of the formation of the hollow microspheres. Thediameter of the bulbous member 23 can be 1.25 to 4 times, preferably 1.5to 3 times and more preferably 1.75 to 2.75 times the diameter of theouter diameter of coaxial blowing nozzle 5. When using a bulbous member23, the transverse jet 13 is aligned such that a line drawn through thecenter axis of transverse jet 13 will pass through the center of bulbousmember 23.

The FIG. 4 illustrates still another embodiment of the invention inwhich a beater bar 24 is used to facilitate detaching of the elongatedcylinder shaped liquid film 12 from the orifice 7a of outer nozzle 7.The beater 24 is attached to a spindle, not shown, which is caused torotate in a manner such that the beater bar 24 is brought to bear uponthe pinched portion 16 of the elongated cylinder 12. The beater bar 24is set to spin at about the same rate as the formtion of hollowmicrospheres and can be 2 to 1500, preferably 10 to 800 and morepreferably 20 to 400 revolutions per second. The beater bar 24 can thusbe used to facilitate the closing off of the cylinder 12 at its innerpinched end 16 and to detach the cylinder 12 from the orifice 7a ofouter nozzle 7.

The FIG. 8 of the drawings illustrates in graphic form the relationshipbetween the thickness of the deposited zinc metal layer, the zinc metalvapor blowing gas pressure and the inside diameter* of the microspheres.The following table indicates the for specific ranges of microspheresizes, the metal vapor blowing gas pressure required to obtain certainthicknesses of deposited metal.

    ______________________________________                                                       Diameter of Metal Vapor                                        Thickness of Deposited                                                                       Microsphere Blowing Gas                                        Metal Layer    (Microns)   Pressure (p.s.i.g.)                                ______________________________________                                         25 to 100A     600-1000   1                                                  100 to 275A    1000-2600   1                                                  275 to 600A    1250-2750   16                                                 600 to 1000A   1250-2250   45                                                 ______________________________________                                    

DESCRIPTION OF THE MICROSPHERES

The hollow microspheres made in accordance with the present inventioncan be made from a wide variety of inorganic film forming materials andcompositions, particularly glass compositions.

The hollow microspheres made in accordance with the present inventioncan be made from suitable inorganic film forming compositions. Thecompositions are preferably resistant to high temperatures and chemicalattack, resistant to corrosive and alkali and resistant to weathering asthe situation may require.

The compositions that can be used are those that have the necessaryviscosities, as mentioned above, when being blown to form stable filmsand which have a rapid change from the molten or liquid state to thesolid or hard state with a relatively narrow temperature change. Thatis, they change from liquid to solid within a relatively narrowlydefined temperature range.

The hollow glass microspheres made in accordance with the presentinvention are preferably made from a low heat conductivity glasscomposition, they are substantially uniform in diameter and wallthickness, have a clear, hard, smooth surface and are resistant tochemical attack, high temperatures and weathering. The hollow glassmicrospheres are substantially uniform in diameter and wall thickness,and depending on their composition and blowing conditions are lighttransparent, translucent or opaque, soft or hard, and smooth or rough.The wall of the microspheres are free or substantially free of anyholes, relatively thinned wall portions or sections, sealing tips,trapped gas bubbles, or sufficient amounts of dissolved gases to formbubbles. The microspheres are also free of any latent solid or liquidblowing gas materials or gases. The preferred glass compositions arethose that are resistant to chemical attack, elevated temperatures,weathering and diffusion of gases into and/or out of the microspheres.Where the blowing gases may decompose at elevated temperatures, glasscompositions that are liquid below the decomposition temperatures of thegases can be used.

The microspheres, because the walls are substantially free of any holes,thinned sections, trapped gas bubbles, and/or sufficient amounts ofdissolved gases to form trapped bubbles are substantially stronger thanthe microspheres heretofore produced. The absence of a sealing tip alsomakes the microsphere stronger.

The microspheres after being formed can be reheated to soften the glassand enlarge the microspheres and/or to improve the surface smoothness ofthe microspheres. On reheating, the internal gas pressure will increaseand cause the microsphere to increase in size. After reheating to thedesired size, for example, in a "shot tower", the microspheres arerapidly cooled to retain the increase in size.

This procedure can in some instances also be used to optimize the metalcrystal size of the deposited metal layer. By carefully controlling thecrystal size growth to produce discontinuites in the deposited metallayer or film, the heat conductivity properties of the metal layer arereduced, while the radiant heat reflecting properties of the metal layerare not adversely affected.

The glass microspheres can be made in various diameters and wallthickness, depending upon the desired end use of the microspheres. Themicrospheres can have an outer diameter of 200 to 10,000 microns,preferably 500 to 6,000 microns and more preferably 1,000 to 4,000microns. The microspheres can have a wall thickness of 0.1 to 1,000microns, preferably 0.5 to 400 microns and more preferably 1 to 100microns.

The microspheres can contain an inert gas at super-atmospheric pressure,about ambient pressure or a partial vacuum. The partial vacuum can beobtained by using a blowing gas which partially condenses within themicrosphere.

The microspheres can contain a high vacuum in the enclosed volume wherea metal vapor is used as a blowing gas and the metal vapor is cooled,condenses and deposits as a thin metal coating on the inner wall surfaceof the hollow microsphere. The pressure in the microsphere will be equalto the vapor pressure of the deposited metal at ambient temperature.

The thickness of the thin metal coating deposited on the inner wallsurface of the microsphere will depend on the metal vapor used to blowthe microsphere, the pressure of the metal vapor and the size of themicrosphere. The thickness of the thin metal coating can be 25 to 1000A, preferably 50 to 600 A, and more preferably 100 to 400 A.

When it is specifically desired that the deposited metal coating betransparent, e.g. to sunlight, the coating should be less than 100 A andpreferably less than 80 A. The transparent metal coated microspheres canhave a deposited metal coating 25 to 95 A and preferably 50 to 80 Athick.

When it is specifically desired that the deposited metal coating bereflective, e.g. to sunlight, the coating should be more than 100 A andpreferably more than 150 A thick. The reflective metal coatedmicrospheres can have a deposited metal coating 105 to 600 A andpreferably 150 to 400 A thick and more preferably 150 to 250 A.

The diameter and wall thickness of the hollow microspheres will ofcourse effect the average bulk density of the microspheres. The glassmicrospheres and glass vacuum microspheres prepared in accordance withthe invention will have an average bulk density of 1 to 15 lb/ft³,preferably 1.5 to 12 lb/ft³ and more preferably 2 to 9 lb/ft³. For usein a preferred embodiment to make low density insulating materials, thehollow glass microspheres can have an average bulk density as low as 0.5to 1.5, for example 1.0 lb/ft³.

Where the microspheres are formed in a manner such that they areconnected by continuous thin glass filaments, that is they are made inthe form of filamented microspheres, the length of the connectingfilaments can be 1 to 40, usually 2 to 20 and more usually 3 to 15 timesthe diameter of the microspheres. The diameter, that is the thickness ofthe connecting filaments, can be 1/5000 to 1/10, usually 1/2500 to 1/20and more usually 1/1000 to 1/30 of the diameter of the microspheres.

The microspheres can contain a gas at superatmospheric pressure, aboutambient pressure or at partial or hard, i.e. high, vacuum.

Where the microspheres are used as insulating materials and ininsulating systems, or in syntactic foam systems, or as filler materialin general, the microspheres can have an outer diameter of 200 to 5,000,preferably 500 to 3,000 and more preferably 750 to 2,000 microns. Themicrospheres can have a wall thickness of 0.1 to 500 microns, preferably0.5 to 200 microns and more preferably 1 to 50 microns. The microspherescan have an average bulk density of 0.3 to 15 lb/ft³, preferably 0.5 to10 lb/ft³ and more preferably 0.75 to 5.0 lb/ft³. When used asinsulating materials, the microspheres can contain a hard vacuum. Whenused as filler materials, the microspheres can have a contained gaspressure of 5 to 100 p.s.i.a., preferably 5 to 75 p.s.i.a. and morepreferably 5 to 12 p.s.i.a.

In a preferred embodiment of the invention, the ratio of the diameter tothe wall thickness of the microspheres is selected such that themicrospheres are flexible, i.e. can be deformed under pressure withoutbreaking.

The microspheres can contain a thin metal layer deposited on the innerwall surface of the microsphere where the blowing gas contains dispersedmetal particles. The thickness of the thin metal coating deposited onthe inner wall surface of the microsphere will depend on the amount andparticle size of the dispersed metal particles or partial pressure oforgano metal blowing gas that are used and the diameter of themicrosphere. The thickness of the thin metal coating can be 25 to 10,000A, preferably 50 to 5,000 A and more preferably 100 to 1,000 A.

When it is desired that the deposited metal coating be transparent tolight, the coating should be less than 100 A and preferably less than 80A. The transparent metal coated microspheres can have a deposited metalcoating 25 to 95 A and preferably 50 to 80 A thick. The microspheres,though transparent to visible light, are substantially reflective ofinfrared radiation.

When it is desired that the deposited metal coating be reflective tolight, the coating can be more than 100 A and preferably more than 150 Athick. The reflective metal coated microspheres can have a depositedmetal coating 105 to 600 A, preferably 150 to 400 A and more preferably150 to 250 A thick.

A particular and advantageous feature of the present invention is thatthe thickness of the thin deposited metal vapor layer can be selectedsuch that the thermal conductivity of the metal forming the metal layerwill be about one-fourth that of the thermal conductivity of the bulkmetal. This substantial reduction in the thermal conductivity of thedeposited metal vapor layer is, however, to some extent effected by themanner in which the metal layer is deposited.

The reduced thermal conductivity effect can be obtained with a depositedmetal thickness of 25 A to 250 A, preferably 50 A to 200 A and morepreferably 75 A to 150 A.

The thermal conductivity of the metal layer can be further reduced bycontrolling the metal layer deposition temperature in a manner such thatmetal crystal growth produces discontinuities in the deposited metalfilm.

The thermal heat conductivity characteristics of heat barriers made fromthe microspheres can be further improved by partially flattening themicrospheres into an oblate spheroid shape. The thermal conductivity ofthe oblate spheroids is further improved by mixing with the oblatespheroids thin glass filaments. The filaments are preferably provided inthe form of the filamented microspheres.

The filamented microspheres can as they are formed by drawn and laid ona conveyor belt or drum. A sufficient amount of tension can bemaintained on the filamented microspheres as they are drawn to stretchthem into the oblate spheroid shape. The filamented microspheres aremaintained in that shape for a sufficient period of time to harden.After hardening of the filamented oblate spheroids, they can be laid ina bed, an adhesive and/or foam can be added and the filamentedmicrospheres can be made into, e.g. a four by eight formed panel. Thepanel can be 1/4 to 3 inches, for example, 1/2, 1, 11/2 or 2 inches, inthickness.

The hollow glass microspheres of the present invention can be used todesign systems having superior insulating characteristics. Where onlyhollow microspheres are used in which the contained volume has an inertlow conductivity gas, systems can be designed in which the thermalconductivity can be as low as R11 per inch, for example, R3 to R11 perinch.

Where only the hollow glass microspheres having a low conductivity gasand low emissivity, reflective metal coating deposited on the inner wallsurface thereof are used, systems can be designed in which the thermalconductivity can be as low as R15 per inch, for example, R5 to R15 perinch.

Where the hollow vacuum microspheres having a low emissivity, highlyreflective metal coating deposited on the inner wall surface thereof areused, systems can be designed in which the thermal conductivity can beas low as R35 per inch, for example, R25 to R35 per inch.

Where an insulating system consisting essentially of hollow glassmicrospheres having a low emissivity, highly reflective metal coatingdeposited on the inner wall surface of the microsphere and a foamedmaterial containing a low heat conductivity gas in the interstices areused, systems can be designed in which the thermal conductivity can beas low as R50 per inch, for example, R30 to R50 per inch.

Where an insulating system consisting essentially of filamented hollowglass vacuum oblate spheroid shaped microspheres having a lowemissivity, highly reflective metal coating deposited on the inner wallsurface of the microspheres and a foamed material containing a low heatconductivity gas in the interstices are used, systems can be designed tohave a thermal conductivity as low as R70 per inch, for example, R40 toR70 per inch.

The microspheres can be used to make heat barriers by filling spacesbetween existing walls or other void spaces or can be made into sheetsor other shaped forms by cementing the microspheres together with asuitable resin or other adhesive or by fusing the microspheres togetherand can be used in new construction.

When the hollow glass microspheres are massed together to form a heatbarrier, there is substantially no heat transfer by solid conductionbecause of the point to point contact between adjacent spheres and thelow conductivity of the glass material used to form the spheres. Thereis little heat transfer by convection because the characteristicdimensions of the voids between the packed spheres are below thatnecessary to initiate convection. There is substantially no heattransfer by gas conduction within the spheres when there is a highvacuum in the enclosed volume since the sphere diameter is smaller thanthe mean free path of the remaining gas molecules. The use of a low heatconductivity gas and/or foam in the interstices between the microspheresalso reduces heat transfer by gas conduction. Where there is a lowemissivity, highly reflective metal layer deposited on the inner wallsurface of the microspheres, there is substantially no radiant heattransfer because of the highly reflective metal layer on the inner wallsurface of the spheres. The primary mode of heat transfer remaining,therefore, is by gas conduction in the interstices or voids between themicrospheres. The overall conductivity of the system is lower than thatof the voids gas or foam because the voids gas or foam occupies only afraction of the volume of the total system, and because conduction pathsthrough the voids gas or foam are attenuated by the presence of thenon-conducting microspheres.

The thermal heat conductivity characteristics of heat barriers made fromthe microspheres can be reduced by filling the interstices between themicrospheres with smaller microspheres of the present invention, a lowthermal conductivity gas, finely divided inert particles, e.g. low heatconductivity foam, e.g. of polyurethane, polyester or polyolefin resinfoam or by enclosing the microspheres in a container and drawing apartial vacuum within the volume of the interstices between themicrospheres.

The hollow glass microspheres of the present invention have a distinctadvantage of being very strong and capable of supporting a substantialamount of weight. They can thus be used to make for the first time asimple inexpensive self-supporting or load bearing vacuum system.

A specific and advantageous use of the hollow glass microspheres hasbeen in the manufacture of insulating systems for use in theconstruction of solar energy collectors.

EXAMPLES EXAMPLE 1

A glass composition comprising the following constituents is used tomake hollow glass microspheres.

    ______________________________________                                        SiO.sub.2  Al.sub.2 O.sub.3                                                                       CaO     MgO    B.sub.2 O.sub.3                                                                     Na.sub.2 O                           ______________________________________                                        Wt %  55-57    18-22    5-7   10-12  4-5   1-2                                ______________________________________                                    

The glass composition is heated to a temperature of 2650° to 2750° F. toform a fluid molten glass having a viscosity of 35 to 60 poises and asurface tension of 275 to 325 dynes per cm.

The molten glass is fed to the apparatus of FIGS. 1 and 2 of thedrawings. The molten glass passes through annular space 8 of blowingnozzle 5 and forms a thin liquid molten glass film across the orifices6a and 7a. The blowing nozzle 5 has an outside diameter of 0.040 inchand orifice 7a has an inside diameter of 0.030 inch. The thin liquidmolten glass film has a diameter of 0.030 inch and a thickness of 0.005inch. An inert blowing gas consisting of xenon or nitrogen at atemperature of 2650° F. and at a positive pressure is applied to theinner surface of the molten glass film causing the film to distenddownwardly into a elongated cylinder shape with its outer end closed andits inner end attached to the outer edge of orifice 7a.

The transverse jet is used to direct an inert entraining fluid whichconsists of nitrogen at a temperature of 2600° F. over and around theblowing nozzle 5 which entraining fluid assists in the formation andclosing of the elongated cylinder shape and the detaching of thecylinder from the blowing nozzle and causing the cylinder to fall freeof the blowing nozzle. The transverse jet is aligned at an angle of 35°to 50° relative to the blowing nozzle and a line drawn through thecenter axis of the transverse jet intersects a line drawn through thecenter axis of the blowing nozzle 5 at a point 2 to 3 times the outsidediameter of the coaxial blowing nozzle 5 above the orifice 7a.

The free falling, i.e. entrained, elongated cylinders quickly assume aspherical shape and are rapidly cooled to about ambient temperature by aquench fluid consisting of a fine water spray at a temperature of 90° to150° F. which quickly cools, solidifies and hardens the glassmicrospheres.

Clear, smooth, hollow glass microspheres having a 2000 to 3000 microndiameter, a 20 to 40 micron wall thickness and filled with xenon ornitrogen gas at an internal contained pressure of 3 p.s.i.a. areobtained. The microspheres are closely examined and are found to be freeof any entrapped bubbles and/or holes and are particularly suitable foruse as filler materials.

EXAMPLE 2

A glass composition comprising the following constituents is used tomake transparent hollow glass vacuum microspheres.

    ______________________________________                                        SiO.sub.2  Al.sub.2 O.sub.3                                                                       CaO     MgO    B.sub.2 O.sub.3                                                                     Na.sub.2 O                           ______________________________________                                        Wt %  55-57    18-22    5-7   10-12  4-5   1-2                                ______________________________________                                    

The glass composition is heated to a temperature of 2650° to 2750° F. toform a fluid molten glass having a viscosity of 35 to 60 poises and asurface tension of 275 to 325 dynes per cm.

The molten glass is fed to the apparatus of FIGS. 1 and 3 of thedrawings. The molten glass is passed through annular space 8 of blowingnozzle 5 and into tapered portion 21 of outer nozzle 7. The molten glassunder pressure is squeezed through a fine gap formed between the outeredge of orifice 6a and the inner surface 22 of the tapered portion 21 ofouter nozzle 7 and forms a thin liquid molten glass film across theorifices 6a and 7a'. The blowing nozzle 5 has an outside diameter of0.04 inch and orifice 7a' has an inside diameter of 0.01 inch. The thinliquid molten glass film has a diameter of 0.01 inch and a thickness of0.003 inch. An inert zinc vapor blowing gas at a temperature of 2700° F.and at a positive pressure is applied to the inner surface of the moltenglass film causing the film to distend outwardly into an elongatedcylinder shape with its outer end closed and its inner end attached tothe outer end of orifice 7a'.

The transverse jet is used to direct an inert entraining fluid whichconsists of nitrogen at a temperature of 2600° F. over and around theblowing nozzle 5 which entraining fluid assists in the formation andclosing of the elongated cylinder shape and detaching of the cylinderfrom the blowing nozzle and causing the cylinder to fall free of theblowing nozzle. The transverse jet is aligned at an angle of 35° to 50°relative to the blowing nozzle and a line drawn through the center axisof the transverse jet intersects a line drawn through the center axis ofthe blowing nozzle 5 at a point 2 to 3 times the outside diameter of thecoaxial blowing nozzle 5 above orifice 7a'.

The free falling elongated cylinders filled with the zinc vapor quicklyassume a spherical shape. The microspheres are contacted with a quenchfluid consisting of a fine water spray at a temperature of 90° to 150°F. which quickly cools, solidifies and hardens the molten glass prior tocooling and condensing the zinc vapor. The zinc vapor begins to condenseat a temperature of about 1660° to 1670° F. at which the glasscomposition used to make the microspheres has already began to hardenand has sufficient strength not to collapse as the zinc vapor begins toand condenses on the inner wall surface of the microsphere (see Tables 2and 3). As the microsphere is further cooled, the zinc vapor condensesand deposits on the inner wall surface of the microsphere as a thin zincmetal coating.

Clear, smooth, hollow glass microspheres having an about 800 to 900micron diameter, a 8 to 20 micron wall thickness and having a thintransparent zinc metal coating 85 to 95 A thick and an internalcontained pressure of 10⁻⁶ Torr are obtained.

EXAMPLE 3

A glass composition comprising the following constituents is used tomake low emissivity, reflective hollow glass vacuum microspheres.

    ______________________________________                                        SiO.sub.2  Al.sub.2 O.sub.3                                                                       CaO     MgO    B.sub.2 O.sub.3                                                                     N.sub.2 O                            ______________________________________                                        Wt %  55-57    18-22    5-7   10-12  4-5   1-2                                ______________________________________                                    

The glass composition is heated to a temperature of 2650° to 2750° F. toform a fluid molten glass having a viscosity of 35 to 60 poises and asurface tension of 275 to 325 dynes per cm.

The molten glass is fed to the apparatus of FIGS. 1 and 3 of thedrawings. The molten glass is passed through annular space 8 of blowingnozzle 5 and into tapered portion 21 of outer nozzle 7. The molten glassunder pressure is squeezed through a fine gap formed between the outeredge of orifice 6a and the inner surface 22 of the tapered portion 21 ofouter nozzle 7 and forms a thin liquid molten glass film across theorifices 6a and 7a'. The blowing nozzle 5 has an outside diameter of0.05 inch and orifice 7a' has an inside diameter of 0.03 inch. The thinliquid molten glass film has a diameter of 0.03 inch and a thickness of0.01 inch. An inert zinc vapor blowing gas at a temperature of 2600° F.and at a positive pressure is applied to the inner surface of the moltenglass film causing the film to distend outwardly into an elongatedcylinder shape with its outer end closed and its inner end attached tothe outer edge of orifice 7a'.

The transverse jet is used to direct an inert entraining fluid whichconsists of nitrogen gas at a temperature of 2500° F. at a linearvelocity of 40 to 100 feet a second over and around the blowing nozzle 5which entraining fluid assists in the formation and closing of theelongated cylinder shape and the detaching of the cylinder from theblowing nozzle and causing the cylinder to fall free of the blowingnozzle. The transverse jet is aligned at an angle of 35° to 50° relativeto the blowing nozzle and a line drawn through the center axis of thetransverse jet intersects a line drawn through the center axis of theblowing nozzle 5 at a point 2 to 3 times the outside diameter of thecoaxial blowing nozzle 5 above orifice 7a'.

The free falling elongated cylinders filled with the zinc vapor quicklyassume a spherical shape. The microspheres are contacted with a quenchfluid consisting of an ethylene glycol spray at a temperature of 0° to15° F. which quickly cools, solidifies and hardens the molten glassprior to cooling and condensing the zinc vapor. The zinc vapor begins tocondense at a temperature of about 1660° to 1670° F. at which the glasscomposition used to make the microspheres has already began to hardenand has sufficient strength not to collapse as the zinc vapor beings toand condenses on the inner wall surface of the microspheres (see Tables2 and 3). As the microsphere is further cooled, the zinc vapor condensesand deposits on the inner wall surface of the microsphere as a thin zincmetal coating.

Clear, smooth, hollow glass microspheres having an about 3000 to 4000micron diameter, a 30 to 40 micron wall thickness and having a lowemissivity, reflective zinc metal coating 325 to 450 A thick and aninternal contained pressure of 10⁻⁶ Torr are obtained.

EXAMPLE 4

A glass composition comprising the following constituents is used tomake low emissivity, reflective hollow glass vacuum filamentedmicrospheres.

    ______________________________________                                        SiO.sub.2  Al.sub.2 O.sub.3                                                                       CaO     MgO    B.sub.2 O.sub.3                                                                     Na.sub.2 O                           ______________________________________                                        Wt %  55-57    18-22    5-7   10-12  4-5   1-2                                ______________________________________                                    

The glass composition is heated to a temperature of 2500° to 2600° F. toform a fluid molten glass having a viscosity of 100 to 200 poises.

The molten glass is fed to the apparatus of FIGS. 1 and 3 of thedrawings under conditions similar to those used in Example 3.

An inert zinc vapor blowing gas at a temperature of 2400° F. and at apositive pressure is applied to the inner surface of the molten glassfilm causing the film to distend outwardly into an elongated cylindershape with its outer end closed and its inner end attached to the outeredge of orifice 7a'.

The transverse jet is used to direct an entraining fluid which consistsof nitrogen gas at a temperature of 2400° F. at a linear velocity of 5to 40 feet a second over and around the blowing nozzle 5 whichentraining fluid assists in the formation and closing of the elongatedcylinder shape and the detaching of the cylinder from the blowing nozzlewhile trailing a thin glass filament which is continuous with the nextmicrosphere forming at the blowing nozzle. The filamented microspheresare otherwise formed in the manner illustrated and described withreference to FIG. 3c of the drawings. The transverse jet is aligned atan angle of 35° to 50° relative to the blowing nozzle and a line drawnthrough the center axis of the transverse jet intersects a line drawnthrough the center axis of the blowing nozzle 5 at a point 2 to 3 timesthe outside diameter of the coaxial blowing nozzle 5 above orifice 7a'.

The entrained elongated filamented cylinder filled with the zinc vaporassumes a spherical shape. The filamented microspheres are contactedwith a quench fluid consisting of water spray at a temperature of 60° to100° F. which quickly cools, solidifies and hardens the molten glassprior to cooling and condensing the zinc vapor after which the zinccondenses on the inner wall surface of the microsphere.

Clear, smooth, hollow filamented glass microspheres having an about 1500to 2500 micron diameter, a 1.5 to 5.0 micron wall thickness and having alow emissivity, reflective zinc metal coating 180 to 275 A thick and aninternal contained pressure of 10⁻⁵ Torr are obtained. The lengths ofthe filament portions of the filamented microspheres is 10 to 20 timesthe diameter of the microspheres. The microspheres are closely examinedand are found to be free of any entrapped bubbles and/or holes.

EXAMPLE 5

A glass composition comprising the following constituents is used tomake low emissivity, reflective hollow glass microspheres containing athin deposited metal layer which is deposited from dispersed metalparticles.

    ______________________________________                                        SiO.sub.2  Al.sub.2 O.sub.3                                                                       CaO     MgO    B.sub.2 O.sub.3                                                                     Na.sub.2 O                           ______________________________________                                        Wt %  55-57    18-22    5-7   10-12  4-5   1-2                                ______________________________________                                    

The glass composition is heated to a temperature of 2650° to 2750° F. toform a fluid molten glass having a viscosity of 35 to 60 poises.

The molten glass is fed to the apparatus of FIGS. 1 and 3 of the drawingunder conditions similar to those used in Example 3.

A blowing gas consisting of argon and containing finely dispersedaluminum particles of 0.03 to 0.05 micron size at a temperature of 2700°F. and at a positive pressure is applied to the inner surface of themolten glass film causing the film to distend outwardly into anelongated cylinder shape with its outer end closed and its inner endattached to the outer edge of orifice 7a'.

The transverse jet is used as before to direct an entraining fluid whichconsists of nitrogen gas at a temperature of 2500° F. over and aroundthe blowing nozzle 5.

The entrained falling elongated cylinders filled with the argon gascontaining the dispersed aluminum particles quickly assume a sphericalshape. The microspheres are contacted with a quench fluid consisting ofan ethylene glycol spray at a temperature of 0° to 15° F. which quicklycools, solidifies and hardens the molten glass. As the mmicrospheres arefurther cooled and hardened, the aluminum particles deposit on the innerwall surface of the microsphere as a thin aluminum metal coating.

Clear, smooth, hollow glass microspheres having an about 1500 to 2500micron diameter, a 5 to 15 micron wall thickness and having a lowemissivity, reflective aluminum metal coating 600 to 1000 A thick and aninternal contained pressure about 5 p.s.i.a. are obtained. Themicrospheres as before are free of any trapped gas bubbles and/or holes.

EXAMPLE 6

An efficient flat plate solar energy collector, as illustrated in FIG. 5of the drawings, is constructed using the glass vacuum microspheres ofthe present invention as a superior insulating material. A solar panelsix feet long and three feet wide and about 31/2 inches thick isconstructed. The outer cover consists of a clear glass or weatherresistant plastic 1/8 inch thick. The two sides, the upper and lowerends of the solar panel are constructed from metal or plastic panelshaving an inner reflective surface. There is disposed within the panelabout mid-way between the top and bottom of the panel a black coatedmetal plate absorber with an absorbance of 0.90 and an emittance of 0.3about 1/8 inch thick to the bottom surface which there are bonded amultiplicity of evenly spaced water heat exchange medium containingtubes. The tubes are of very thin wall construction and can have anoutside diameter of about one inch. These tubes can also have a blackcoating. Suitable inlets and outlets are provided for the heat exchangemedium.

The solar panel has an inner cover member about 1/8 to 1/4 inch thick bymeans of which the panel can be attached to the roof of a home. Theinner cover member can be made from metal or plastic and can have aninner reflective surface.

In accordance with the present invention, the area between the outercover and the upper surface of the black coated metal absorber plate isfilled to a depth of about one inch with transparent glass vacuummicrospheres made by the method of Example 2 of about 800 microndiameter, 10 micron wall thickness and having a thin transparent zincmetal coating about 85 A thick and an internal contained pressure of10⁻⁶ Torr.

The area between the lower surface of the black coated metal absorberplate and the inner cover member is filled to a depth of about 11/2inches with the reflective glass vacuum microspheres made by the methodof Example 3 of about 3000 micron diameter, 30 micron wall thickness andhaving a thin low emissivity, reflective zinc metal coating 325 A thickand an internal contained pressure of 10⁻⁶ Torr.

The solar panel has suitable inlet and outlet means for the water heatexchange medium. On a bright sunny day with an outside temperature of90° F., it is found that inlet water at a temperature of 80° F. isheated under pressure to an outlet temperature of 280° F. An outlettemperature of 280° F. is more than sufficient for summerair-conditioning needs. The outlet temperature of 280° F. is to becontrasted with a water outlet temperature of about 160° F. produced byconventional solar panels.

The same solar panel on a bright sunny day with an outside temperatureof 32° F., it is found that inlet water at a temperature of 80° F. isheated to an outlet temperature of 180° F. An outlet temperature of 180°F. is more than sufficient for winter household heating and hot waterrequirements.

EXAMPLE 7

An efficient tubular solar energy collector, as illustrated in FIG. 6 ofthe drawings, is constructed using the glass vacuum microspheres of thepresent invention as a superior insulating material. A tubular solarcollector six feet in length and about 41/4 inches in diameter isconstructed. The outer cover consists of a clear glass or weatherresistant plastic 1/2 inch thick. The two parallel sides and the lowercurved portion are constructed from metal or plastic about 1/8 inchthick. The lower curved portion is coated with a highly reflectivesurface for reflecting and concentrating the sun's rays towards thecenter of the tubular collector. The tubular collector has end membersclosing the opposite ends constructed to similar material to that of thesides and lower curved portion which are also about 1/8 inch thick.

There is disposed within the solar collector and concentric to the lowercurved portion of the collector a double pipe tubular member consistingof a thin walled inner feed tube and a thin walled outer return tube.The inner feed tube is coaxial to the outer return tube. The outerreturn tube has on its outer surface a black heat absorbing coating ofthe type described in Example 6. The inner feed tube can be one inch indiameter and the outer return tube can be two inches in diameter.

The tubular collectors are normally mounted in parallel in a manner suchthat they intercept the movement of the sun across the sky. Inaccordance with the present invention, the area between the outer cover,the sides and the lower curved portion and the double pipe tubularmember is filled with transparent glass vacuum microspheres made by themethod of Example 2 to provide an about one inch layer of transparentvacuum microspheres completely around the double pipe tubular member.

The transparent glass vacuum microspheres are 800 microns in diameter,have a wall thickness of 10 microns and a thin transparent zinc metalcoating 85 A thick and contain an internal pressure of 10⁻⁶ Torr.

The tubular solar energy collector has a suitable inlet and outlet meansfor a water heat exchange medium. On a bright sunny day with an outsidetemperature of 90° F., it is found that inlet water at a temperature of80° F., on a single pass, is heated to an outlet temperature of 240° F.An outlet temperature of 240° F. is more than sufficient for summerair-conditioning needs. The same tubular solar energy collector on abright sunny day with an outside temperature of 32° F., it is found thatinlet water at a temperature of 80° F. is heated to an outlettemperature of 170° F. An outlet temperature of 170° F. is more thansufficient for winter household heating and hot water requirements.

EXAMPLE 8

The FIG. 7 of the drawings illustrates the use of the hollow glassmicrospheres of the present invention in the construction of a one-inchthick formed wall panel. The wall panel contains multiple layers ofuniform size glass microspheres made by the method of Example 4 of theinvention. The microspheres have a 1500 to 2500, e.g. 2000, microndiameter, a 1.5 to 5.0, e.g. 2.0, micron wall thickness and a thin, lowemissivity zinc metal coating 180 A to 275 A, e.g. 250 A, thickdeposited on the inner wall surface of the microsphere and an internalcontained pressure of 10⁻⁵ Torr.

The interstices between the microspheres is filled with low heatconductivity foam containing Freon-11 gas. The microspheres are treatedwith a thin adhesive coating and formed into a 7/8 inch thick layer. Theadhesive is allowed to cure to form a semi-rigid wall board. The facingsurface of the wall board is coated with an about 1/8 inch thick plasterwhich is suitable for subsequent sizing and painting and/or coveringwith wall paper. The backing surface of the panel is coated with anabout 1/16 inch coating of a suitable plastic composition to form avapor seal. The final panels are allowed to cure. The cured panels formstrong wall panels which can be sawed and nailed and readily used inconstruction of new homes. Several sections of the panels are tested andfound to have a R value of 30 per inch.

EXAMPLE 9

The FIG. 7b of the drawings illustrates the use of the filamented hollowglass microspheres of the present invention in the construction of aformed wall panel one-inch thick. The wall panel contains hollow glassmicrospheres made by the method of Example 4. The microspheres have a1500 to 2500, e.g. 2000, micron diameter, a 1.5 to 5.0, e.g. 2.0, micronwall thickness and a thin, low emissivity zinc metal coating 180 A to275 A, e.g. 250 A, thick deposited on the inner wall surface of themicrosphere and an internal contained pressure of 10⁻⁵ Torr. A low heatconductivity resin adhesive foam containing Freon-11 gas is mixed withthe microspheres and formed into a layer one-inch thick and pressed andflattened between two flat plates to form the microspheres into anoblate spheroid shape in which the ratio of the height to length of theflattened microspheres is about 1:3. The flattened microspheres are heldin this position until the adhesive foam resin surrounding themicrospheres cures after which microspheres retain their flattenedshape.

The interstices between the microspheres are thus filled with a low heatconductivity foam containing Freon-11 gas. The facing surface of thewall board is about 1/8 inch plaster which is suitable for subsequentsizing and painting and/or covering with wall paper. The backing of thewall panel is about a 1/16 inch coating of plastic which forms a vaporseal. The panels are cured and form strong wall panels which can besawed and nailed and readily used in construction of new homes. Severalsections of the panel are tested and found to have a R value of 50 perinch.

EXAMPLE 10

The formed panels of Examples 8 and 9 can also be made to have a densitygradient in the direction of the front to back of the panel. Where thepanel is used indoors the surface facing the room can be made to have arelatively high density and high strength, by increasing the proportionof resin or other binder to microspheres. The surface facing the outsidecan be made to have relatively low density and a high insulation barriereffect by having a high proportion of microspheres to resin or binder.For example, the front one-third of the panel can have an averagedensity of about two to three times that of the average density of thecenter third of the panel.

The density of the back one-third of the panel can be about one-half toone-third that of the center third of the panel. Where the panels areused on the outside of a house, the sides of the panel can be reversed,i.e. the high density side can face outward.

UTILITY

The hollow glass microspheres of the present invention have many usedincluding the manufacture of superior insulating materials and the useof the microspheres as a filler or aggregate in cement, plaster andasphalt and synthetic construction board materials. The microspheres canalso be used in the manufacture of insulated louvers and molded objectsor forms.

The microsphere can be used to form thermal insulation barriers merelyby filling spaces between the walls of refrigerator trucks or traincars, household refrigerators, cold storage building facilities, homes,factories and office buildings.

The hollow microspheres can be produced from inorganic film formingmaterials and compositions, from glass compositions and from highmelting temperature glass compositions, and when used as a component inbuilding construction retard the development and expansion of fires. Thehollow microspheres and glass microspheres, depending on the compositionfrom which made, are stable to many chemical agents and weatheringconditions.

The microspheres can be bonded together by sintering or suitable resinadhesives and molded into sheets or other forms and used in newconstructions which require thermal insulation including homes,factories and office buildings. The construction materials made from themicrospheres can be preformed or made at the construction site.

The microspheres may be adhered together with known adhesives or bindersto produce semi- or rigid cellular type materials for use inmanufacturing various products or in construction. The microspheres,because they are made from very stable glass compositions, are notsubject to degradation by outgassing, aging, moisture, weathering orbiological attack and do not produce toxic fumes when exposed to veryhigh temperatures or fire. The hollow glass microspheres when used inmanufacture of superior insulating materials can advantageously be usedalone or in combination with fiberglass, styrofoam, polyurethane foam,phenol-formaldehyde foam, organic and inorganic binders and the like.

The microspheres of the present invention can be used to make insulatingindustrial tapes and insulating, wallboard and ceiling tiles. Themicrospheres can also advantageously be used in plastic or resin boatconstruction to produce high strength hulls and/or hulls whichthemselves are buoyant.

The glass compositions can also be selected to produce microspheres thatwill be selectively permeable to specific gases and/or organicmolecules. These microspheres can then be used as semi-permeablemembranes to separate gaseous or liquid mixtures.

The process and apparatus of the present invention as mentioned abovecan be used to blow microspheres from suitable inorganic film formingmaterials or compositions having sufficient viscosity at the temperatureat which the microspheres are blown to form a stable elongated cylindershape of the material being blown and to subsequently be detached toform the spherical shaped microspheres and on cooling to form a hardenedfilm.

The glass compositions can be transparent, translucent or opaque. Asuitable coloring material can be added to the glass compositions to aidin identification of microspheres of specified size, wall thickness andcontained gaseous material.

In carrying out the process of the present invention, the glass materialto be used to form the microspheres is selected and can be treatedand/or mixed with other materials to adjust their viscosity and surfacetension characteristics such that at the desired blowing temperaturesthey are capable of forming hollow microspheres of the desired size andwall thickness.

The process and apparatus described herein can also be used toencapsulate and store gaseous material in hollow glass microspheres of asuitable non-interacting composition, thereby allowing storage orhandling of gases generally, and of corrosive and toxic or otherwisehazardous gases specifically. Because of their small size and relativegreat strength, the gases may be encapsulated into hollow microspheresat elevated pressures, thus allowing high pressure storage of thesegases. In the case where disposal by geological storage is desired, forexample for poisonous and/or other toxic gases, the gases can beencapsulated in very durable alumina silicate or zirconia glassmicrospheres which can subsequently be embedded, if desired, in aconcrete structure. The glass microspheres of the present invention,because they can be made to contain gases under high pressure, can beused to manufacture fuel targets for laser fusion reactor systems.

The process and apparatus of the invention can also be used to formhollow microspheres from metals such as iron, steel, nickel, gold,copper, zinc, tin, brass, lead, aluminum and magnesium. In order to formmicrospheres from these materials, suitable additives are used whichprovide at the surface of a blown microsphere a sufficiently highviscosity that a stable microsphere can be formed.

The process of the present invention can also be carried out in acentrifuge apparatus in which the coaxial blowing nozzles are disposedin the outer circumferal surface of the centrifuge. Liquid glass is fedinto the centrifuge and because of centrifugal forces rapidly coats andwets the inner wall surface of the outer wall of the centrifuge. Theliquid glass is fed into the outer coaxial nozzle. The inlet to theinner coaxial nozzle is disposed above the coating of liquid glass. Theblowing gas is as before fed into the inner coaxial nozzle. Thetransverse jet entraining fluid is provided by transverse jets mountedon the outer surface of the rotating bowl. An external gas can bedirected along the longitudinal axis of the centrifuge to assist inremoving the microspheres from the vicinity of the centrifuge as theyare formed. Quench fluids can be provided as before.

These and other uses of the present invention will become apparent tothose skilled in the art from the foregoing description and thefollowing appended claims.

It will be understood that various changes and modifications may be madein the invention, and that the scope thereof is not to be limited exceptas set forth in the claims.

I claim:
 1. Hollow inorganic film forming material microspheres ofsubstantially uniform diameter of 200 to 10,000 microns and ofsubstantially uniform wall thickness of 0.1 to 1,000 microns, whereinsaid microspheres are free of latent solid or liquid blowing gasmaterials or gases and the walls of said microspheres are substantiallyfree of holes, relatively thinned wall portions or sections, sealingtips and bubbles.
 2. Hollow inorganic film forming material microspheresof substantially uniform diameter of 500 to 6,000 microns and ofsubstantially uniform wall thickness of 0.5 to 400 microns, wherein saidmicrospheres are free of latent solid or liquid blowing gas materials orgases and the walls of said microspheres are substantially free ofholes, relatively thinned wall portions or sections, sealing tips andbubbles.
 3. The hollow microspheres of claim 2 having a contained gaspressure of 5 to 100 p.s.i.a.
 4. The hollow microspheres of claim 2having deposited on the inner wall surfaces thereof a thin metal coating50 to 600° A. thick.
 5. The hollow microspheres of claim 2 having adiameter of 500 to 3,000 microns and a wall thickness of 0.5 to 200microns.
 6. The hollow microspheres of claim 2 wherein the microsphereshave an average bulk density of 0.5 to 10 lb/ft³.
 7. A mass of themicrospheres of claim
 2. 8. The hollow microspheres of claim 2 having anoblate spheroid shape.
 9. Filamented, hollow inorganic film formingmaterial microspheres of substantially uniform diameter of 200 to 10,000microns and of substantially uniform wall thickness of 0.1 to 1000microns, wherein said microspheres are connected to each other byfilament portions which are continuous with the microspheres and are ofthe same inorganic film forming material from which the microspheres aremade, and said microspheres are free of latent solid or liquid blowinggas materials or gases, and the walls of said microspheres aresubstantially free of holes, relatively thinned wall portions orsections and bubbles.
 10. Filamented, hollow inorganic film formingmaterial microspheres of substantially uniform diameter of 500 to 6000microns and of substantially uniform wall thickness of 0.5 to 400microns, wherein said microspheres are connected to each other byfilament portions which are continuous with the microspheres and are ofthe same inorganic film forming material from which the microspheres aremade, and said microspheres are free of latent solid or liquid blowinggas materials or gases, and the walls of said microspheres aresubstantially free of holes, relatively thinned wall portions orsections and bubbles.
 11. The hollow microspheres of claim 10 whereinthe length of the connecting filaments is substantially equal and is 2to 20 times the diameter of the microspheres.
 12. The hollowmicrospheres of claim 10 wherein the length of the connecting filamentsis substantially equal and the diameter of the connecting filaments is1/2500 to 1/20 the diameter of the microspheres.
 13. Hollow glassmicrospheres of substantially uniform diameter of 200 to 10,000 micronsand of substantially uniform wall thickness of 0.1 to 1,000 microns,wherein said microspheres are free of latent solid or liquid blowing gasmaterials or gases and the walls of said microspheres are substantiallyfree of holes, relatively thinned wall portions or sections, sealingtips and bubbles.
 14. Hollow glass microspheres of substantially uniformdiameter of 500 to 6,000 microns and of substantially uniform wallthickness of 0.5 to 400 microns, wherein said microspheres are free oflatent solid or liquid blowing gas materials or gases and the walls ofsaid microspheres are substantially free of holes, relatively thinnedwall portions or sections, sealing tips and bubbles.
 15. The hollowmicrospheres of claim 14 having a contained gas pressure of 5 to 100p.s.i.a.
 16. The hollow microspheres of claim 14 having a thin metalcoating deposited on the inner wall surfaces of the microspheresconsisting of a layer of dispersed metal particles 50 to 5000° A thick.17. The hollow microspheres of claim 14 having deposited on the innerwall surfaces thereof a thin metal coating 50 to 600° A thick.
 18. Thehollow microspheres of claim 14 having a high contained vacuum of 10⁻⁴to 10⁻⁶ Torrs.
 19. The hollow microspheres of claim 17 wherein thedeposited metal is zinc less than 100° A thick and is transparent tovisible light.
 20. The hollow microspheres of claim 17 wherein thedeposited metal is zinc more than 100° A thick and is reflective ofvisible light.
 21. The hollow microspheres of claim 14 having a diameterof 500 to 3000 microns and a wall thickness of 0.5 to 200 microns. 22.The hollow microspheres of claim 14 having an average bulk density of0.5 to 10 lb/ft³.
 23. A mass of the microspheres of claim
 14. 24. Thehollow microspheres of claim 14 having an oblate spheroid shape.
 25. Thehollow glass microspheres of claim 14 wherein there is deposited on theinner wall surfaces a thin metal transparent coating 25 to 95° A thick.26. The hollow glass microspheres of claim 14 wherein there is depositedon the inner wall surfaces thereof a thin metal reflective coating 105to 800° A thick.
 27. The hollow microspheres of claim 14 wherein themicrospheres have a high contained vacuum of 10⁻⁴ to 10⁻⁶ Torrs and havedeposited on the inner wall surfaces thereof a thin metal coatingconsisting of metallic zinc 180 to 275° A thick.
 28. The hollowmicrospheres of claim 14 wherein the microspheres have a high containedvacuum of 10⁻⁴ to 10⁻⁶ Torrs and have deposited on the inner wallsurfaces thereof a thin metal coating 150 to 400° A thick. 29.Filamented, hollow glass microspheres of substantially uniform diameterof 200 to 10,000 microns and of substantially uniform wall thickness of0.1 to 1000 microns, wherein said microspheres are connected to eachother by filament portions which are continuous with the microspheresand are of the same inorganic film forming material from which themicrospheres are made, and said microspheres are free of latent solid orliquid blowing gas materials or gases and the walls of said microspheresare substantially free of holes, relatively thinned wall portions orsections and bubbles.
 30. Filamented, hollow glass microspheres ofsubstantially uniform diameter of 500 to 6000 microns and ofsubstantially uniform wall thickness of 0.5 to 400 microns, wherein saidmicrospheres are connected to each other by filament portions which arecontinuous with the microspheres and are of the same inorganic filmforming material from which the microspheres are made, and saidmicrospheres are free of latent solid or liquid blowing gas materials orgases, and the walls of said microspheres are substantially free ofholes, relatively thinned wall portions or sections and bubbles.
 31. Thehollow microspheres of claim 30 having a contained gas pressure of 5 to100 p.s.i.a.
 32. The hollow microspheres of claim 30 having deposited onthe inner wall surfaces thereof a thin metal coating 50 to 600° A thick.33. The hollow microspheres of claim 30 having a high contained vacuumof 10⁻⁴ to 10⁻⁶ Torrs.
 34. The hollow microspheres of claim 32 whereinthe deposited metal is zinc less than 100° A thick and is transparent tovisible light.
 35. The hollow microspheres of claim 32 wherein thedeposited metal is zinc more than 100° A thick and is reflective ofvisible light.
 36. A mass of the microspheres of claim
 30. 37. Thehollow microspheres of claim 30 having an oblate spheroid shape.
 38. Thehollow microspheres of claim 30 wherein the length of the connectingfilaments is substantially equal and is 2 to 20 times the diameter ofthe microspheres.
 39. The hollow microspheres of claim 30 wherein thelength of the connecting filaments is substantially equal and thediameter of the connecting filament is 1/2500 to 1/20 the diameter ofthe microspheres.
 40. Filamented, hollow inorganic film forming materialmicrospheres having a diameter of 200 to 10,000 microns and having awall thickness of 0.1 to 1000 microns, wherein said microspheres areconnected to each other by filament portions which are continuous withthe microspheres and are the same inorganic film forming material fromwhich the microspheres are made.
 41. Filamented, hollow inorganic filmforming material microspheres having a diameter of 500 to 6000 micronsand having a wall thickness of 0.5 to 400 microns, wherein saidmicrospheres are connected to each other by filament portions which arecontinuous with the microspheres and are of the same inorganic filmforming material from which the microspheres are made.
 42. Filamented,hollow glass microspheres having a diameter of 200 to 10,000 microns andhaving a wall thickness of 0.1 to 1,000 microns, wherein saidmicrospheres are connected to each other by filament portions which arecontinuous with the microspheres and are of the same inorganic filmforming material from which the microspheres are made.
 43. Filamented,hollow glass microspheres having a uniform diameter of 500 to 6,000microns and having a wall thickness of 0.5 to 400 microns, wherein saidmicrospheres are connected to each other by filament portions which arecontinuous with the microspheres and are of the same inorganic filmforming material from which the microspheres are made.